🌊 MermaidsGrade 5Reading: grades 5-6Place valueAdditionSubtractionMultiplicationDivision
The Mystery of the Coral Cavern
A mysterious intruder swam into the Royal Grotto and snatched the Great Pearl of Coral Cove! Detective Finn needs your help to decode the evidence and unmask the culprit.
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 | Tail Magic | Artifact | Wrist Cuff | Scale Color | Weakness |
|---|---|---|---|---|---|
| Thalassa | kelp whip | prism trident | right arm cuff | sapphire scales | bright sunlight |
| Ronne | sonic song | sea glass ring | right arm cuff | emerald scales | bright sunlight |
| Waverly | current burst | starfish star | left arm cuff | ruby scales | bright sunlight |
| Coralie | bubble shield | pearl wand | right arm cuff | emerald scales | bright sunlight |
| Triton | bubble shield | starfish star | left arm cuff | sapphire scales | bright sunlight |
| Cordelia | tide wave | sea glass ring | right arm cuff | sapphire scales | bright sunlight |
| Nerida | tide wave | starfish star | right arm cuff | sapphire scales | bright sunlight |
| Marina | tide wave | starfish star | right arm cuff | emerald scales | bright sunlight |
| Electra | kelp whip | pearl wand | right arm cuff | sapphire scales | dry sponge |
| Reef | kelp whip | shell compass | right arm cuff | ruby scales | loud applause |
| Kailani | tide wave | starfish star | left arm cuff | sapphire scales | bright sunlight |
| Nixie | tide wave | prism trident | left arm cuff | emerald scales | loud applause |
| Delphine | kelp whip | shell compass | right arm cuff | sapphire scales | bright sunlight |
| Nautilus | current burst | shell compass | left arm cuff | ruby scales | bright sunlight |
| Caspian | sonic song | shell compass | left arm cuff | ruby scales | bright sunlight |
| Tursi | sonic song | shell compass | left arm cuff | emerald scales | dry sponge |
| Harbor | current burst | pearl wand | right arm cuff | sapphire scales | bright sunlight |
| Finnegan | bubble shield | pearl wand | left arm cuff | sapphire scales | bright sunlight |
| Pearl | sonic song | pearl wand | right arm cuff | emerald scales | loud applause |
| Calder | bubble shield | shell compass | left arm cuff | ruby scales | bright sunlight |
| Oceanus | kelp whip | starfish star | left arm cuff | sapphire scales | loud applause |
Clue 1
Place value
The guard examined the glowing sonar readout to check the target digit position.
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
5000
9000
200
3000
800
700
700
30
800
50
400
60
200
90
50
60
T
5000
600
90
200
30
90
9000
200
700
700
2000
60
1000
8000
30
90
90
What is the value of the 5 in 825,968?T
What is the value of the 7 in 889,793?L
What is the value of the 2 in 917,294?E
What is the value of the 9 in 680,596?S
What is the value of the 3 in 240,239?A
What is the value of the 8 in 958,940?P
What is the value of the 4 in 89,462?D
What is the value of the 1 in 301,979?M
What is the value of the 8 in 51,854?I
What is the value of the 3 in 13,025?V
What is the value of the 2 in 82,936?C
What is the value of the 9 in 69,441?H
What is the value of the 5 in 313,257?N
What is the value of the 6 in 70,695?U
What is the value of the 6 in 18,564?O
0/15 letters found
Clue 2
Addition
Detective Finn tallied up the total number of glowing pearls collected across the reef sectors.
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
5486
8712
2454
9472
6553
9472
9228
2454
6931
T
5486
7959
8187
3130
2454
7457
9472
8712
9513
5482
8297
6931
6553
3304
3304
8187
5482
T
5486
8712
2454
3130
9513
6231
8712
T
5486
7457
3130
5788
3771 + 1715 =T
1730 + 3752 =N
4224 + 3233 =A
5600 + 3628 =P
2619 + 4312 =C
4601 + 3696 =Y
1556 + 1574 =R
3122 + 3431 =U
3259 + 4700 =W
5163 + 3024 =O
6051 + 3421 =S
3738 + 2050 =M
4619 + 4894 =I
1198 + 2106 =F
5525 + 3187 =H
1256 + 1198 =E
2126 + 4105 =G
0/17 letters found
Clue 3
Subtraction
The guards calculated the remaining distance after subtracting the speed of the ocean currents.
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
1723
4932
8912
8518
4738
8912
8563
8483
3476
T
1723
4932
6343
8912
2504
8518
4932
4752
8563
4738
8483
2621
8563
6787
8483
2504
4752
8321
8101
2621
4752
6343
3615
4932
T
1723
8518
1261
4738
1073
6343
3615
4932
T
1723
6712 - 4989 =T
7812 - 2880 =H
11872 - 3551 =O
8820 - 4082 =N
10002 - 1901 =M
11279 - 2761 =S
9211 - 728 =K
10162 - 1599 =A
8918 - 2131 =C
6418 - 2803 =G
2883 - 262 =B
3424 - 920 =F
10043 - 3700 =I
4767 - 3506 =U
5038 - 3965 =L
6008 - 2532 =Y
7242 - 2490 =R
9381 - 469 =E
0/18 letters found
Clue 4
Multiplication facts (1-12)
The squad organized the kelp patrols into equal rows to compute the total search area.
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
14
5
72
72
66
54
33
32
S
14
15
5
36
32
S
14
S
14
66
54
80
80
32
33
32
144
54
11
12
66
32
S
14
32
5
30
32
144
S
14
5
11
144
7 × 2 =S
3 × 5 =C
12 × 12 =D
1 × 5 =A
6 × 9 =I
4 × 8 =E
10 × 8 =M
1 × 12 =T
5 × 6 =B
6 × 6 =L
6 × 12 =P
3 × 11 =R
11 × 1 =N
6 × 11 =H
0/14 letters found
Clue 5
Division facts (1-12) — the last clue
The reef team split the total treasure chests equally among the safe vaults.
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
20 ÷ 4 = ?
100 ÷ 10 = ?
9 ÷ 1 = ?
11 ÷ 11 = ?
12 ÷ 3 = ?
28 ÷ 4 = ?
84 ÷ 7 = ?
36 ÷ 12 = ?
8 ÷ 4 = ?
8 ÷ 1 = ?
48 ÷ 8 = ?
Step 2 — cross out the sentence with each answer
1.The villain swung a kelp whip, then consulted a shell compass.
2.The villain cast a bubble shield, then glowing with a sea glass ring.
3.The villain cast a bubble shield, then waved a pearl wand.
4.The villain swung a kelp whip, then glowing with a sea glass ring.
5.The villain created a tide wave, then glowing with a sea glass ring.
6.The villain summoned a current burst, then threw a starfish star.
7.The villain swung a kelp whip, then threw a starfish star.
8.The villain summoned a current burst, then glowing with a sea glass ring.
9.The villain created a tide wave, then threw a starfish star.
10.The villain summoned a current burst, then waved a pearl wand.
11.The villain swung a kelp whip, then flashed a prism trident.
12.The villain blasted a sonic song, then glowing with a sea glass ring.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Mystery of the Coral Cavern
Culprit: Thalassa (kelp whip · prism trident · right arm cuff · sapphire scales · bright sunlight)
- Clue 1 (Place value): "THE VILLAIN DOES NOT USE A SHELL COMPASS"What is the value of the 5 in 825,968? = 5000 (T) · What is the value of the 7 in 889,793? = 700 (L) · What is the value of the 2 in 917,294? = 200 (E) · What is the value of the 9 in 680,596? = 90 (S) · What is the value of the 3 in 240,239? = 30 (A) · What is the value of the 8 in 958,940? = 8000 (P) · What is the value of the 4 in 89,462? = 400 (D) · What is the value of the 1 in 301,979? = 1000 (M) · What is the value of the 8 in 51,854? = 800 (I) · What is the value of the 3 in 13,025? = 3000 (V) · What is the value of the 2 in 82,936? = 2000 (C) · What is the value of the 9 in 69,441? = 9000 (H) · What is the value of the 5 in 313,257? = 50 (N) · What is the value of the 6 in 70,695? = 600 (U) · What is the value of the 6 in 18,564? = 60 (O)
- Clue 2 (Addition): "THE SUSPECT WORE A SHINY CUFF ON THE RIGHT ARM"3771 + 1715 = 5486 (T) · 1730 + 3752 = 5482 (N) · 4224 + 3233 = 7457 (A) · 5600 + 3628 = 9228 (P) · 2619 + 4312 = 6931 (C) · 4601 + 3696 = 8297 (Y) · 1556 + 1574 = 3130 (R) · 3122 + 3431 = 6553 (U) · 3259 + 4700 = 7959 (W) · 5163 + 3024 = 8187 (O) · 6051 + 3421 = 9472 (S) · 3738 + 2050 = 5788 (M) · 4619 + 4894 = 9513 (I) · 1198 + 2106 = 3304 (F) · 5525 + 3187 = 8712 (H) · 1256 + 1198 = 2454 (E) · 2126 + 4105 = 6231 (G)
- Clue 3 (Subtraction): "THE SNEAKY THIEF SHRANK BACK FROM BRIGHT SUNLIGHT"6712 - 4989 = 1723 (T) · 7812 - 2880 = 4932 (H) · 11872 - 3551 = 8321 (O) · 8820 - 4082 = 4738 (N) · 10002 - 1901 = 8101 (M) · 11279 - 2761 = 8518 (S) · 9211 - 728 = 8483 (K) · 10162 - 1599 = 8563 (A) · 8918 - 2131 = 6787 (C) · 6418 - 2803 = 3615 (G) · 2883 - 262 = 2621 (B) · 3424 - 920 = 2504 (F) · 10043 - 3700 = 6343 (I) · 4767 - 3506 = 1261 (U) · 5038 - 3965 = 1073 (L) · 6008 - 2532 = 3476 (Y) · 7242 - 2490 = 4752 (R) · 9381 - 469 = 8912 (E)
- Clue 4 (Multiplication facts (1-12)): "SAPPHIRE SCALES SHIMMERED IN THE SEABED SAND"7 × 2 = 14 (S) · 3 × 5 = 15 (C) · 12 × 12 = 144 (D) · 1 × 5 = 5 (A) · 6 × 9 = 54 (I) · 4 × 8 = 32 (E) · 10 × 8 = 80 (M) · 1 × 12 = 12 (T) · 5 × 6 = 30 (B) · 6 × 6 = 36 (L) · 6 × 12 = 72 (P) · 3 × 11 = 33 (R) · 11 × 1 = 11 (N) · 6 × 11 = 66 (H)
- Clue 5 (Division facts (1-12)): surviving statement (box 11) → Thalassa20 ÷ 4 = 5 · 100 ÷ 10 = 10 · 9 ÷ 1 = 9 · 11 ÷ 11 = 1 · 12 ÷ 3 = 4 · 28 ÷ 4 = 7 · 84 ÷ 7 = 12 · 36 ÷ 12 = 3 · 8 ÷ 4 = 2 · 8 ÷ 1 = 8 · 48 ÷ 8 = 6
About this mystery
- Grade level
- Grade 5 math
- Math topics
- Place value, Addition, Subtraction, Multiplication, Division
- Reading level
- grades 5-6
- Theme
- The Mystery of the Coral Cavern — set in Coral Cove Castle
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects