Grade 1Reading: grades 1-2AdditionSubtractionSkip countingPlace valueMissing addends
The Secret Treehouse Mystery
The Golden Compass is missing from our treehouse! A sneaky Trickster took it. We must find who did it before the sun goes down.
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 | Favorite Tool | Secret Gadget | Flashlight Hand | Hair Color | Dropped Clue |
|---|---|---|---|---|---|
| Finn | Super Magnet | Jet Pack | Left Handed | Red Hair | Fruit Snacks |
| Zoe | Super Magnet | Bouncy Boots | Left Handed | Brown Hair | Fruit Snacks |
| Quinn | Super Magnet | Water Blaster | Right Handed | Blonde Hair | Fruit Snacks |
| Luke | Grappling Hook | Pocket Drone | Right Handed | Blonde Hair | Juice Boxes |
| Dan | Spy Camera | Pocket Drone | Left Handed | Red Hair | Juice Boxes |
| Lily | Grappling Hook | Pocket Drone | Left Handed | Blonde Hair | Fruit Snacks |
| Toby | Spy Camera | Water Blaster | Right Handed | Blonde Hair | Shiny Coins |
| Kate | Spy Camera | Bouncy Boots | Left Handed | Red Hair | Juice Boxes |
| Grace | Spy Camera | Night Goggles | Left Handed | Blonde Hair | Shiny Coins |
| Cody | Laser Pointer | Jet Pack | Left Handed | Brown Hair | Fruit Snacks |
| Mia | Grappling Hook | Bouncy Boots | Left Handed | Brown Hair | Shiny Coins |
| Sam | Spy Camera | Jet Pack | Right Handed | Blonde Hair | Shiny Coins |
| Hugo | Super Magnet | Water Blaster | Right Handed | Blonde Hair | Shiny Coins |
| Owen | Grappling Hook | Night Goggles | Left Handed | Brown Hair | Fruit Snacks |
| Emma | Walkie Talkie | Bouncy Boots | Right Handed | Blonde Hair | Shiny Coins |
| Noah | Grappling Hook | Pocket Drone | Right Handed | Blonde Hair | Shiny Coins |
| Leo | Spy Camera | Pocket Drone | Right Handed | Red Hair | Shiny Coins |
| Jack | Spy Camera | Bouncy Boots | Right Handed | Brown Hair | Juice Boxes |
| Ruby | Spy Camera | Night Goggles | Right Handed | Red Hair | Fruit Snacks |
| Piper | Laser Pointer | Water Blaster | Right Handed | Red Hair | Shiny Coins |
| Iris | Super Magnet | Water Blaster | Left Handed | Red Hair | Shiny Coins |
Clue 1
Addition
We need to count our magnifying glasses. We found four on the table and five in the drawer. How many do we have in all?
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
8
15
11
T
8
15
20
11
4
6
10
11
14
19
10
T
8
15
17
3
11
2
10
7
19
16
18
2
10
10
T
8
14
3 + 5 =T
10 + 8 =Y
7 + 3 =O
11 + 4 =H
1 + 1 =B
10 + 6 =C
3 + 1 =F
11 + 6 =A
1 + 2 =V
6 + 13 =N
4 + 7 =E
2 + 4 =D
10 + 10 =I
5 + 2 =U
7 + 7 =S
0/15 letters found
Clue 2
Subtraction
We had ten walkie talkie batteries, but we dropped three into the creek. How many batteries do we have 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.
T
2
12
11
T
2
12
6
11
13
12
11
15
14
T
2
12
11
15
6
16
12
T
2
6
5
T
2
12
11
6
4
4
6
16
12
T
2
12
9
5
14
8 - 6 =T
13 - 8 =N
19 - 3 =G
18 - 6 =H
15 - 9 =I
9 - 5 =R
19 - 5 =D
17 - 4 =F
20 - 5 =L
17 - 8 =A
16 - 5 =E
0/11 letters found
Clue 3
Skip counting
We see flashlight footprints in pairs. Let us count the boots by twos to see how many kids walked here.
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
10
65
90
28
26
60
14
6
6
90
26
120
65
36
70
28
55
14
36
70
120
20
28
T
10
65
90
T
10
60
90
90
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, ___, 12, 14T
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, ___, 22, 24B
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110E
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42I
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, ___, 16, 18O
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32Y
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, ___, 130, 140S
Skip-count by 2s. Fill the blank: 2, 4, ___, 8, 10P
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, ___, 80, 90N
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30D
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65C
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75H
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, ___, 65, 70R
0/13 letters found
Clue 4
Place value
The spy decoder screen shows a secret code. It has one ten and seven ones. What number is the decoder showing?
Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.
W
71
34
40
34
52
34
93
52
34
40
67
81
63
37
75
52
51
54
37
76
40
34
63
67
60
75
What number has 7 tens and 1 one?W
What number has 7 tens and 6 ones?N
What number has 5 tens and 1 one?B
What number has 5 tens and 2 ones?T
What number has 6 tens and 7 ones?A
What number has 3 tens and 4 ones?E
What number has 5 tens and 4 ones?L
What number has 6 tens and 0 ones?I
What number has 9 tens and 3 ones?C
What number has 3 tens and 7 ones?O
What number has 7 tens and 5 ones?R
What number has 8 tens and 1 one?S
What number has 4 tens and 0 ones?D
What number has 6 tens and 3 ones?H
0/14 letters found
Clue 5
Missing addends — the last clue
We need eight gold coins to open the lock. We only found five coins so far. How many more coins do we need?
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
2 + ___ = 9
8 + ___ = 14
2 + ___ = 4
2 + ___ = 10
9 + ___ = 21
1 + ___ = 2
5 + ___ = 14
3 + ___ = 14
4 + ___ = 7
7 + ___ = 11
8 + ___ = 13
Step 2 — cross out the sentence with each answer
1.The villain uses the grappling hook to climb up, then sprays water from the water blaster.
2.The villain uses the grappling hook to climb up, then launches the pocket drone.
3.The villain pulls the keys with the super magnet, then flies away on the jet pack.
4.The villain calls for backup on the walkie talkie, then sprays water from the water blaster.
5.The villain calls for backup on the walkie talkie, then launches the pocket drone.
6.The villain snaps a photo with the spy camera, then flies away on the jet pack.
7.The villain snaps a photo with the spy camera, then sprays water from the water blaster.
8.The villain calls for backup on the walkie talkie, then jumps high with the bouncy boots.
9.The villain snaps a photo with the spy camera, then launches the pocket drone.
10.The villain pulls the keys with the super magnet, then sprays water from the water blaster.
11.The villain uses the grappling hook to climb up, then flies away on the jet pack.
12.The villain shines the bright laser pointer, then launches the pocket drone.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Secret Treehouse Mystery
Culprit: Hugo (Super Magnet · Water Blaster · Right Handed · Blonde Hair · Shiny Coins)
- Clue 1 (Addition): "THE THIEF DOES NOT HAVE BOUNCY BOOTS"3 + 5 = 8 (T) · 10 + 8 = 18 (Y) · 7 + 3 = 10 (O) · 11 + 4 = 15 (H) · 1 + 1 = 2 (B) · 10 + 6 = 16 (C) · 3 + 1 = 4 (F) · 11 + 6 = 17 (A) · 1 + 2 = 3 (V) · 6 + 13 = 19 (N) · 4 + 7 = 11 (E) · 2 + 4 = 6 (D) · 10 + 10 = 20 (I) · 5 + 2 = 7 (U) · 7 + 7 = 14 (S)
- Clue 2 (Subtraction): "THE THIEF HELD THE LIGHT IN THEIR RIGHT HAND"8 - 6 = 2 (T) · 13 - 8 = 5 (N) · 19 - 3 = 16 (G) · 18 - 6 = 12 (H) · 15 - 9 = 6 (I) · 9 - 5 = 4 (R) · 19 - 5 = 14 (D) · 17 - 4 = 13 (F) · 20 - 5 = 15 (L) · 17 - 8 = 9 (A) · 16 - 5 = 11 (E)
- Clue 3 (Skip counting): "THEY DROPPED SHINY COINS BY THE TREE"Skip-count by 2s. Fill the blank: 2, 4, 6, 8, ___, 12, 14 = 10 (T) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, ___, 22, 24 = 20 (B) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110 = 90 (E) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42 = 36 (I) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, ___, 16, 18 = 14 (O) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32 = 28 (Y) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, ___, 130, 140 = 120 (S) · Skip-count by 2s. Fill the blank: 2, 4, ___, 8, 10 = 6 (P) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, ___, 80, 90 = 70 (N) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30 = 26 (D) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65 = 55 (C) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75 = 65 (H) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, ___, 65, 70 = 60 (R)
- Clue 4 (Place value): "WE DETECTED A SHORT BLONDE HAIR"What number has 7 tens and 1 one? = 71 (W) · What number has 7 tens and 6 ones? = 76 (N) · What number has 5 tens and 1 one? = 51 (B) · What number has 5 tens and 2 ones? = 52 (T) · What number has 6 tens and 7 ones? = 67 (A) · What number has 3 tens and 4 ones? = 34 (E) · What number has 5 tens and 4 ones? = 54 (L) · What number has 6 tens and 0 ones? = 60 (I) · What number has 9 tens and 3 ones? = 93 (C) · What number has 3 tens and 7 ones? = 37 (O) · What number has 7 tens and 5 ones? = 75 (R) · What number has 8 tens and 1 one? = 81 (S) · What number has 4 tens and 0 ones? = 40 (D) · What number has 6 tens and 3 ones? = 63 (H)
- Clue 5 (Missing addends): surviving statement (box 10) → Hugo2 + ___ = 9 = 7 · 8 + ___ = 14 = 6 · 2 + ___ = 4 = 2 · 2 + ___ = 10 = 8 · 9 + ___ = 21 = 12 · 1 + ___ = 2 = 1 · 5 + ___ = 14 = 9 · 3 + ___ = 14 = 11 · 4 + ___ = 7 = 3 · 7 + ___ = 11 = 4 · 8 + ___ = 13 = 5
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 Secret Treehouse Mystery — set in The Secret Treehouse
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects