Grade 1Reading: grades 1-2AdditionSubtractionSkip countingPlace valueMissing addends
The Island Treehouse Mystery
Someone hid the golden scout trophy inside the treehouse! Help the Island Explorers find out who took it before sunset.
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 | Island Tool | Badge | Watch Hand | Cap Color | Snack Counter |
|---|---|---|---|---|---|
| Cole | torch beam | star badge | wears watch on left wrist | red cap | scared of crunchy apples |
| Ava | torch beam | star badge | wears watch on left wrist | blue cap | scared of sour lemons |
| Max | rope launcher | moon badge | wears watch on right wrist | green cap | scared of crunchy apples |
| Luke | torch beam | leaf badge | wears watch on left wrist | red cap | scared of crunchy apples |
| Jack | torch beam | star badge | wears watch on left wrist | red cap | scared of sour lemons |
| Leo | rope launcher | star badge | wears watch on right wrist | blue cap | scared of crunchy apples |
| Ivy | rope launcher | star badge | wears watch on right wrist | green cap | scared of crunchy apples |
| Chloe | rope launcher | wave badge | wears watch on right wrist | red cap | scared of crunchy apples |
| Maya | bamboo net | moon badge | wears watch on right wrist | green cap | scared of salty pretzels |
| Toby | glider wings | leaf badge | wears watch on right wrist | red cap | scared of sour lemons |
| Mia | rope launcher | wave badge | wears watch on left wrist | blue cap | scared of sour lemons |
| Aria | bamboo net | leaf badge | wears watch on left wrist | red cap | scared of crunchy apples |
| Sam | glider wings | wave badge | wears watch on right wrist | blue cap | scared of sour lemons |
| Kai | torch beam | leaf badge | wears watch on right wrist | blue cap | scared of sour lemons |
| Owen | torch beam | leaf badge | wears watch on left wrist | green cap | scared of crunchy apples |
| Nora | compass map | moon badge | wears watch on left wrist | red cap | scared of crunchy apples |
| Eli | bamboo net | wave badge | wears watch on right wrist | red cap | scared of crunchy apples |
| Noah | glider wings | star badge | wears watch on left wrist | blue cap | scared of crunchy apples |
| Ella | compass map | leaf badge | wears watch on right wrist | blue cap | scared of salty pretzels |
| Lily | rope launcher | sun badge | wears watch on left wrist | red cap | scared of crunchy apples |
| Finn | torch beam | star badge | wears watch on right wrist | blue cap | scared of sour lemons |
Clue 1
Addition
We gathered up all the lost trail maps. Let us add them together to find the first clue.
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
17
3
15
16
7
15
4
13
6
9
19
10
10
4
19
7
12
20
15
16
7
20
T
17
3
4
9
15
4
16
11
7
14
4
12
2
15
11 + 6 =T
1 + 1 =G
7 + 8 =E
2 + 2 =A
4 + 8 =D
6 + 7 =K
13 + 7 =O
4 + 12 =S
6 + 8 =B
5 + 2 =N
2 + 1 =H
3 + 8 =U
2 + 4 =Y
2 + 7 =V
6 + 13 =I
5 + 5 =L
0/16 letters found
Clue 2
Subtraction
Some gear went missing from the camp chest. Subtract the lost items to see what is left.
Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.
A
19
16
14
3
1
9
8
8
8
A
19
16
A
19
16
A
19
3
2
4
13
1
3
4
9
5
9
7
3
16
10
14
8
3
20 - 1 =A
17 - 8 =E
6 - 4 =C
19 - 6 =O
18 - 4 =I
3 - 2 =N
6 - 2 =H
8 - 3 =L
15 - 8 =F
18 - 2 =W
5 - 2 =T
16 - 6 =R
10 - 2 =S
0/13 letters found
Clue 3
Skip counting
We found rows of footprints in the sand. Let us skip count by fives to track the trail.
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
90
39
100
42
21
140
140
33
21
55
25
33
55
33
36
33
6
28
25
80
18
30
25
65
55
30
39
6
33
14
14
140
100
10
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110T
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, ___, 30, 35R
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, ___, 24, 27I
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42W
Skip-count by 10s. Fill the blank: 10, 20, ___, 40, 50C
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, ___, 42, 45H
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, ___, 90, 100O
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120E
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, ___, 150, 160L
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, ___, 12, 14S
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32F
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75U
Skip-count by 2s. Fill the blank: 2, 4, ___, 8, 10Y
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48V
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, ___, 20, 22M
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, ___, 16, 18P
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39A
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65N
0/18 letters found
Clue 4
Place value
The digital scout sign flashes numbers in tens and ones. Look closely at the place value to read the message.
Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.
E
83
96
63
43
E
83
36
34
E
83
73
68
99
34
E
83
36
E
83
99
52
88
61
99
73
81
E
83
43
34
73
57
What number has 8 tens and 3 ones?E
What number has 8 tens and 1 one?R
What number has 5 tens and 7 ones?P
What number has 5 tens and 2 ones?H
What number has 7 tens and 3 ones?A
What number has 8 tens and 8 ones?O
What number has 3 tens and 6 ones?N
What number has 6 tens and 3 ones?I
What number has 3 tens and 4 ones?C
What number has 9 tens and 6 ones?V
What number has 6 tens and 1 one?W
What number has 4 tens and 3 ones?D
What number has 9 tens and 9 ones?S
What number has 6 tens and 8 ones?T
0/14 letters found
Clue 5
Missing addends — the last clue
We have eight coconut bowls but we need twelve in total. Find the missing number to solve the last puzzle.
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
4 + ___ = 9
6 + ___ = 14
5 + ___ = 17
4 + ___ = 15
9 + ___ = 13
2 + ___ = 5
1 + ___ = 7
6 + ___ = 15
7 + ___ = 14
1 + ___ = 2
8 + ___ = 10
Step 2 — cross out the sentence with each answer
1.The villain soared on glider wings, then showed off a star badge.
2.The villain soared on glider wings, then flashed a sun badge.
3.The villain fired the rope launcher, then wore a moon badge.
4.The villain shined the torch beam, then wore a moon badge.
5.The villain shined the torch beam, then showed off a star badge.
6.The villain checked the compass map, then showed off a star badge.
7.The villain fired the rope launcher, then pinned on a leaf badge.
8.The villain threw the bamboo net, then pinned on a leaf badge.
9.The villain threw the bamboo net, then showed off a star badge.
10.The villain shined the torch beam, then pinned on a leaf badge.
11.The villain fired the rope launcher, then flashed a sun badge.
12.The villain checked the compass map, then wore a moon badge.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Island Treehouse Mystery
Culprit: Luke (torch beam · leaf badge · wears watch on left wrist · red cap · scared of crunchy apples)
- Clue 1 (Addition): "THE SNEAKY VILLAIN DOES NOT HAVE A SUN BADGE"11 + 6 = 17 (T) · 1 + 1 = 2 (G) · 7 + 8 = 15 (E) · 2 + 2 = 4 (A) · 4 + 8 = 12 (D) · 6 + 7 = 13 (K) · 13 + 7 = 20 (O) · 4 + 12 = 16 (S) · 6 + 8 = 14 (B) · 5 + 2 = 7 (N) · 2 + 1 = 3 (H) · 3 + 8 = 11 (U) · 2 + 4 = 6 (Y) · 2 + 7 = 9 (V) · 6 + 13 = 19 (I) · 5 + 5 = 10 (L)
- Clue 2 (Subtraction): "A WITNESS SAW A WATCH ON THE LEFT WRIST"20 - 1 = 19 (A) · 17 - 8 = 9 (E) · 6 - 4 = 2 (C) · 19 - 6 = 13 (O) · 18 - 4 = 14 (I) · 3 - 2 = 1 (N) · 6 - 2 = 4 (H) · 8 - 3 = 5 (L) · 15 - 8 = 7 (F) · 18 - 2 = 16 (W) · 5 - 2 = 3 (T) · 16 - 6 = 10 (R) · 10 - 2 = 8 (S)
- Clue 3 (Skip counting): "THE VILLAIN RAN AWAY FROM CRUNCHY APPLES"Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110 = 90 (T) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, ___, 30, 35 = 25 (R) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, ___, 24, 27 = 21 (I) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42 = 36 (W) · Skip-count by 10s. Fill the blank: 10, 20, ___, 40, 50 = 30 (C) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, ___, 42, 45 = 39 (H) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, ___, 90, 100 = 80 (O) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120 = 100 (E) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, ___, 150, 160 = 140 (L) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, ___, 12, 14 = 10 (S) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32 = 28 (F) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75 = 65 (U) · Skip-count by 2s. Fill the blank: 2, 4, ___, 8, 10 = 6 (Y) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48 = 42 (V) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, ___, 20, 22 = 18 (M) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, ___, 16, 18 = 14 (P) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39 = 33 (A) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65 = 55 (N)
- Clue 4 (Place value): "EVIDENCE AT SCENE SHOWS A RED CAP"What number has 8 tens and 3 ones? = 83 (E) · What number has 8 tens and 1 one? = 81 (R) · What number has 5 tens and 7 ones? = 57 (P) · What number has 5 tens and 2 ones? = 52 (H) · What number has 7 tens and 3 ones? = 73 (A) · What number has 8 tens and 8 ones? = 88 (O) · What number has 3 tens and 6 ones? = 36 (N) · What number has 6 tens and 3 ones? = 63 (I) · What number has 3 tens and 4 ones? = 34 (C) · What number has 9 tens and 6 ones? = 96 (V) · What number has 6 tens and 1 one? = 61 (W) · What number has 4 tens and 3 ones? = 43 (D) · What number has 9 tens and 9 ones? = 99 (S) · What number has 6 tens and 8 ones? = 68 (T)
- Clue 5 (Missing addends): surviving statement (box 10) → Luke4 + ___ = 9 = 5 · 6 + ___ = 14 = 8 · 5 + ___ = 17 = 12 · 4 + ___ = 15 = 11 · 9 + ___ = 13 = 4 · 2 + ___ = 5 = 3 · 1 + ___ = 7 = 6 · 6 + ___ = 15 = 9 · 7 + ___ = 14 = 7 · 1 + ___ = 2 = 1 · 8 + ___ = 10 = 2
About this mystery
- Grade level
- Grade 1 math
- Math topics
- Addition, Subtraction, Skip counting, Place value, Missing addends
- Reading level
- grades 1-2
- Theme
- The Island Treehouse Mystery — set in Sunken Coconut Cove
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects