🌊 MermaidsGrade 5Reading: grades 5-6RoundingSkip countingWord problemsMulti-step word problemsMissing addends
The Case of the Missing Neptune Crown
The shimmering Neptune Crown has vanished from the royal treasury of Coral Cove! Five suspects were spotted near the vault reef. Analyze the clues left in the sea currents to unmask the culprit before they escape into the deep trench.
Suspects
Possible suspects
Cross off a row as each clue rules it out. On screen, tap a row.
21 of 21 still in play
| Name | Primary Magic | Secondary Skill | Dominant Flipper | Tail Fin Style | Banishing Relic |
|---|---|---|---|---|---|
| Marina | Bubble Shield | Shark Whisper | Right Flipper | Ocean Blue Fin | Sea Salt Crystal |
| Riptide | Bioluminescence | Shark Whisper | Right Flipper | Coral Pink Fin | Golden Trident |
| Nautilus | Bioluminescence | Dolphin Telepathy | Right Flipper | Kelp Green Fin | Sea Salt Crystal |
| Finley | Wave Blast | Crab Summoning | Right Flipper | Coral Pink Fin | Golden Trident |
| Nerida | Tide Control | Dolphin Telepathy | Right Flipper | Coral Pink Fin | Golden Trident |
| Zephyr | Wave Blast | Dolphin Telepathy | Left Flipper | Ocean Blue Fin | Sea Salt Crystal |
| Coralia | Tide Control | Dolphin Telepathy | Right Flipper | Kelp Green Fin | Golden Trident |
| Shelly | Tide Control | Whale Song Call | Right Flipper | Coral Pink Fin | Golden Trident |
| Cascade | Wave Blast | Eel Camouflage | Right Flipper | Coral Pink Fin | Golden Trident |
| Posey | Bioluminescence | Shark Whisper | Left Flipper | Ocean Blue Fin | Golden Trident |
| Glaucus | Current Whirl | Crab Summoning | Right Flipper | Kelp Green Fin | Sea Salt Crystal |
| Siren | Wave Blast | Dolphin Telepathy | Right Flipper | Kelp Green Fin | Golden Trident |
| Serena | Wave Blast | Dolphin Telepathy | Left Flipper | Kelp Green Fin | Polished Pearl |
| Pearl | Tide Control | Dolphin Telepathy | Right Flipper | Ocean Blue Fin | Golden Trident |
| Kai | Bubble Shield | Dolphin Telepathy | Right Flipper | Coral Pink Fin | Polished Pearl |
| Delphine | Current Whirl | Dolphin Telepathy | Left Flipper | Kelp Green Fin | Golden Trident |
| Triton | Current Whirl | Shark Whisper | Right Flipper | Ocean Blue Fin | Golden Trident |
| Abyss | Bioluminescence | Crab Summoning | Left Flipper | Coral Pink Fin | Golden Trident |
| Urchin | Bubble Shield | Eel Camouflage | Right Flipper | Coral Pink Fin | Polished Pearl |
| Thalassa | Bubble Shield | Whale Song Call | Right Flipper | Ocean Blue Fin | Polished Pearl |
| Calypso | Bioluminescence | Shark Whisper | Right Flipper | Coral Pink Fin | Polished Pearl |
Clue 1
Rounding
The vault guard sonar system only displays rounded depth numbers to simplify navigation logs.
Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.
T
430
1700
5000
900
2000
9000
9000
3700
2000
130
30
2900
5000
200
130
2900
T
430
290
200
5000
7000
1700
3700
9000
5000
200
2900
130
300
700
3700
9000
9000
Round 432 to the nearest tenT
Round 656 to the nearest hundredC
Round 288 to the nearest tenU
Round 232 to the nearest hundredS
Round 306 to the nearest hundredG
Round 1,669 to the nearest thousandI
Round 9,259 to the nearest thousandL
Round 3,672 to the nearest hundredA
Round 2,946 to the nearest hundredO
Round 6,509 to the nearest thousandW
Round 1,675 to the nearest hundredH
Round 31 to the nearest tenD
Round 4,522 to the nearest thousandE
Round 134 to the nearest tenN
Round 861 to the nearest hundredV
0/15 letters found
Clue 2
Skip counting
A trail of glow-algae pulses at steady rhythmic intervals down the trench path.
Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.
S
20
130
15
30
26
S
20
S
20
55
16
130
18
55
9
22
39
26
24
30
15
18
S
20
130
100
110
30
15
40
55
18
42
26
15
24
24
9
30
42
15
30
S
20
18
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, ___, 22, 24S
Skip-count by 3s. Fill the blank: 3, 6, ___, 12, 15E
Skip-count by 10s. Fill the blank: 10, 20, 30, ___, 50, 60G
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150W
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65H
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, ___, 21, 24T
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48F
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26C
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, ___, 120, 130M
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, ___, 18, 20O
Skip-count by 5s. Fill the blank: 5, 10, ___, 20, 25I
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, ___, 42, 45U
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, ___, 35, 40R
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120A
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, ___, 27, 30P
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30L
0/16 letters found
Clue 3
Word problems
The chief mermaid archivist cataloged the missing clam shells stored in the vault.
Solve each problem to learn its letter, then write the letters in the boxes to fill in the missing word.
Someonescaredthevillainoffwith .
G
83
18
75
106
11
96
99
R
I
106
11
96
99
Reef Guard found 9 kelp scrolls yesterday and 74 more today. How many kelp scrolls in all?G
There were 15 polished conch shells. 4 were used up. How many polished conch shells are left?E
Reef Guard lined up 8 rows of 12 glowing pearls. How many glowing pearls in all?N
Reef Guard found 10 kelp scrolls yesterday and 8 more today. How many kelp scrolls in all?O
Reef Guard found 23 polished conch shells yesterday and 52 more today. How many polished conch shells in all?L
There were 127 starfish badges. 28 were used up. How many starfish badges are left?T
There were 121 sea glass tokens. 15 were used up. How many sea glass tokens are left?D
0/7 letters found
Clue 4
Multi-step word problems
Reef patrol units spent two shifts calculating total sea glass tokens left near the crime scene.
Solve each problem to learn its letter, then write the letters in the boxes to fill in the missing word.
Astrandof hairturnedupatthescene.
C
79
60
63
36
86
75
16
N
K
F
16
N
Reef Guard earned 2 starfish badges in each of 3 rounds, plus 78 bonus starfish badges. Then 5 starfish badges were lost. How many starfish badges are left?C
There were 503 polished conch shells in all. 23 polished conch shells were set aside. The rest were shared equally among 8 Coral Patrol. How many polished conch shells did each get?O
Reef Guard filled 2 boxes with 9 starfish badges each, then found 18 more starfish badges. How many starfish badges are there in all?A
There were 445 glowing pearls in all. 15 glowing pearls were set aside. The rest were shared equally among 5 Coral Patrol. How many glowing pearls did each get?L
Reef Guard collected 275 starfish badges in the morning and 103 starfish badges in the afternoon, then split them equally among 6 Coral Patrol. How many starfish badges did each get?R
There were 90 glowing pearls in all. 2 Coral Patrol used 5 glowing pearls each. The other 5 Coral Patrol shared the rest equally. How many glowing pearls did each of the other Coral Patrol get?I
Reef Guard filled 2 boxes with 6 kelp scrolls each, then found 63 more kelp scrolls. How many kelp scrolls are there in all?P
0/7 letters found
Clue 5
Missing addends — the last clue
The mermaid guard ledger shows missing inventory spaces that must be calculated to balance the record.
First solve each problem. Then find each answer in the list below and cross that sentence out. One sentence will be left — that's exactly what the villain did!
Step 1 — solve these
31 + ___ = 43
2 + ___ = 3
34 + ___ = 40
10 + ___ = 19
24 + ___ = 32
26 + ___ = 30
3 + ___ = 8
5 + ___ = 8
39 + ___ = 50
4 + ___ = 11
40 + ___ = 50
Step 2 — cross out the sentence with each answer
1.The villain fired a massive wave blast, then blended in like an eel.
2.The villain fired a massive wave blast, then commanded guard crabs.
3.The villain raised a bubble shield, then signaled nearby dolphins.
4.The villain summoned a high tide, then blended in like an eel.
5.The villain spun a whirlpool, then commanded guard crabs.
6.The villain flashed blinding lights, then calmed patrolling sharks.
7.The villain flashed blinding lights, then commanded guard crabs.
8.The villain summoned a high tide, then commanded guard crabs.
9.The villain fired a massive wave blast, then called the deep whales.
10.The villain raised a bubble shield, then blended in like an eel.
11.The villain fired a massive wave blast, then calmed patrolling sharks.
12.The villain summoned a high tide, then signaled nearby dolphins.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Case of the Missing Neptune Crown
Culprit: Finley (Wave Blast · Crab Summoning · Right Flipper · Coral Pink Fin · Golden Trident)
- Clue 1 (Rounding): "THE VILLAIN DOES NOT USE WHALE SONG CALL"Round 432 to the nearest ten = 430 (T) · Round 656 to the nearest hundred = 700 (C) · Round 288 to the nearest ten = 290 (U) · Round 232 to the nearest hundred = 200 (S) · Round 306 to the nearest hundred = 300 (G) · Round 1,669 to the nearest thousand = 2000 (I) · Round 9,259 to the nearest thousand = 9000 (L) · Round 3,672 to the nearest hundred = 3700 (A) · Round 2,946 to the nearest hundred = 2900 (O) · Round 6,509 to the nearest thousand = 7000 (W) · Round 1,675 to the nearest hundred = 1700 (H) · Round 31 to the nearest ten = 30 (D) · Round 4,522 to the nearest thousand = 5000 (E) · Round 134 to the nearest ten = 130 (N) · Round 861 to the nearest hundred = 900 (V)
- Clue 2 (Skip counting): "SWIRLS SHOW THE CULPRIT SWAM RIGHT FLIPPER FIRST"Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, ___, 22, 24 = 20 (S) · Skip-count by 3s. Fill the blank: 3, 6, ___, 12, 15 = 9 (E) · Skip-count by 10s. Fill the blank: 10, 20, 30, ___, 50, 60 = 40 (G) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150 = 130 (W) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65 = 55 (H) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, ___, 21, 24 = 18 (T) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48 = 42 (F) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26 = 22 (C) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, ___, 120, 130 = 110 (M) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, ___, 18, 20 = 16 (O) · Skip-count by 5s. Fill the blank: 5, 10, ___, 20, 25 = 15 (I) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, ___, 42, 45 = 39 (U) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, ___, 35, 40 = 30 (R) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120 = 100 (A) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, ___, 27, 30 = 24 (P) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30 = 26 (L)
- Clue 3 (Word problems): "GOLDEN TRIDENT"Reef Guard found 9 kelp scrolls yesterday and 74 more today. How many kelp scrolls in all? = 83 (G) · There were 15 polished conch shells. 4 were used up. How many polished conch shells are left? = 11 (E) · Reef Guard lined up 8 rows of 12 glowing pearls. How many glowing pearls in all? = 96 (N) · Reef Guard found 10 kelp scrolls yesterday and 8 more today. How many kelp scrolls in all? = 18 (O) · Reef Guard found 23 polished conch shells yesterday and 52 more today. How many polished conch shells in all? = 75 (L) · There were 127 starfish badges. 28 were used up. How many starfish badges are left? = 99 (T) · There were 121 sea glass tokens. 15 were used up. How many sea glass tokens are left? = 106 (D)
- Clue 4 (Multi-step word problems): "CORAL PINK FIN"Reef Guard earned 2 starfish badges in each of 3 rounds, plus 78 bonus starfish badges. Then 5 starfish badges were lost. How many starfish badges are left? = 79 (C) · There were 503 polished conch shells in all. 23 polished conch shells were set aside. The rest were shared equally among 8 Coral Patrol. How many polished conch shells did each get? = 60 (O) · Reef Guard filled 2 boxes with 9 starfish badges each, then found 18 more starfish badges. How many starfish badges are there in all? = 36 (A) · There were 445 glowing pearls in all. 15 glowing pearls were set aside. The rest were shared equally among 5 Coral Patrol. How many glowing pearls did each get? = 86 (L) · Reef Guard collected 275 starfish badges in the morning and 103 starfish badges in the afternoon, then split them equally among 6 Coral Patrol. How many starfish badges did each get? = 63 (R) · There were 90 glowing pearls in all. 2 Coral Patrol used 5 glowing pearls each. The other 5 Coral Patrol shared the rest equally. How many glowing pearls did each of the other Coral Patrol get? = 16 (I) · Reef Guard filled 2 boxes with 6 kelp scrolls each, then found 63 more kelp scrolls. How many kelp scrolls are there in all? = 75 (P)
- Clue 5 (Missing addends): surviving statement (box 2) → Finley31 + ___ = 43 = 12 · 2 + ___ = 3 = 1 · 34 + ___ = 40 = 6 · 10 + ___ = 19 = 9 · 24 + ___ = 32 = 8 · 26 + ___ = 30 = 4 · 3 + ___ = 8 = 5 · 5 + ___ = 8 = 3 · 39 + ___ = 50 = 11 · 4 + ___ = 11 = 7 · 40 + ___ = 50 = 10
About this mystery
- Grade level
- Grade 5 math
- Math topics
- Rounding, Skip counting, Word problems, Multi-step word problems, Missing addends
- Reading level
- grades 5-6
- Theme
- The Case of the Missing Neptune Crown — set in Coral Cove Kingdom
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects