Grade 1Reading: grades 1-2AdditionSubtractionSkip countingPlace valueMissing addends
The Great Treehouse Mystery
Someone took our Golden Binoculars from the treehouse! We must follow the footprints in the mud to find who did it. Let us solve the clues together.
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 | Special Gear | Adventure Badge | Writing Hand | Cap Color | Silly Fear |
|---|---|---|---|---|---|
| Meg | spy glass | tent badge | righty grip | red cap | scared of spiders |
| Ruby | walkie talkie | rope badge | righty grip | green cap | scared of frogs |
| Sam | decoder ring | rope badge | righty grip | green cap | scared of frogs |
| Rex | walkie talkie | fire badge | righty grip | red cap | scared of frogs |
| Zoe | spy glass | fire badge | righty grip | red cap | scared of frogs |
| Max | decoder ring | map badge | lefty grip | blue cap | scared of shadows |
| Luke | decoder ring | star badge | righty grip | green cap | scared of frogs |
| Joy | decoder ring | fire badge | lefty grip | green cap | scared of frogs |
| Toby | flashlight | map badge | righty grip | green cap | scared of spiders |
| Abby | spy glass | fire badge | lefty grip | red cap | scared of shadows |
| Leo | walkie talkie | tent badge | righty grip | red cap | scared of frogs |
| Amy | walkie talkie | tent badge | righty grip | green cap | scared of frogs |
| Ned | decoder ring | star badge | lefty grip | green cap | scared of spiders |
| Dan | climbing rope | rope badge | righty grip | blue cap | scared of shadows |
| Mia | climbing rope | rope badge | lefty grip | blue cap | scared of spiders |
| Roy | spy glass | tent badge | lefty grip | red cap | scared of spiders |
| Jon | spy glass | rope badge | lefty grip | red cap | scared of frogs |
| Lily | decoder ring | map badge | lefty grip | green cap | scared of shadows |
| Ben | walkie talkie | map badge | righty grip | green cap | scared of frogs |
| Emma | walkie talkie | star badge | lefty grip | red cap | scared of frogs |
| Jake | flashlight | star badge | righty grip | red cap | scared of shadows |
Clue 1
Addition
We found a pile of map pins. Let us count how many red ones and blue ones we have in total.
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
16
13
6
18
2
10
10
11
2
3
8
7
6
9
3
7
T
16
13
11
18
6
T
16
13
6
T
16
6
3
T
16
4
11
8
15
6
11 + 5 =T
1 + 2 =N
7 + 4 =A
8 + 10 =V
2 + 7 =S
5 + 2 =O
4 + 11 =G
1 + 5 =E
2 + 2 =B
1 + 1 =I
4 + 6 =L
3 + 10 =H
3 + 5 =D
0/13 letters found
Clue 2
Subtraction
We had some juice boxes, but some got drank. Let us subtract to see how many are 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
12
16
10
14
16
10
7
11
T
12
16
10
15
10
17
2
1
T
12
16
6
9
1
18
16
T
12
14
18
9
1
15
17 - 5 =T
9 - 3 =A
18 - 8 =E
7 - 6 =I
16 - 1 =P
11 - 2 =R
20 - 2 =G
19 - 2 =N
17 - 6 =D
15 - 8 =L
7 - 5 =W
16 - 2 =Y
17 - 1 =H
0/13 letters found
Clue 3
Skip counting
Look at the rows of muddy boot prints. Let us count them by twos to follow the 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.
T
26
130
22
42
100
16
15
16
45
16
42
45
130
22
15
16
12
100
27
36
50
55
90
33
22
25
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30T
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42G
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110M
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48Y
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, ___, 30, 33O
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, ___, 18, 20A
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39P
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120R
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, ___, 60, 70J
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65U
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, ___, 30, 35D
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, ___, 14, 16F
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, ___, 50, 55W
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150H
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26E
Skip-count by 5s. Fill the blank: 5, 10, ___, 20, 25N
0/16 letters found
Clue 4
Place value
The secret code box has a screen showing tens and ones. Let us find the real number.
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
77
73
19
68
24
22
33
95
46
94
73
73
22
91
95
93
19
50
70
73
94
49
73
94
73
What number has 7 tens and 7 ones?W
What number has 9 tens and 3 ones?P
What number has 2 tens and 4 ones?U
What number has 6 tens and 8 ones?O
What number has 2 tens and 2 ones?N
What number has 7 tens and 3 ones?E
What number has 5 tens and 0 ones?I
What number has 4 tens and 9 ones?H
What number has 3 tens and 3 ones?D
What number has 7 tens and 0 ones?B
What number has 4 tens and 6 ones?G
What number has 9 tens and 1 one?C
What number has 9 tens and 5 ones?A
What number has 9 tens and 4 ones?R
What number has 1 ten and 9 ones?F
0/15 letters found
Clue 5
Missing addends — the last clue
The badge box holds ten badges. Some are missing. Let us find how many we need to fill it.
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
9 + ___ = 17
4 + ___ = 15
4 + ___ = 6
10 + ___ = 15
8 + ___ = 11
1 + ___ = 10
3 + ___ = 7
2 + ___ = 9
1 + ___ = 2
8 + ___ = 14
8 + ___ = 18
Step 2 — cross out the sentence with each answer
1.The villain shines a flashlight around, then polishes a rope badge.
2.The villain talks on a walkie talkie, then polishes a rope badge.
3.The villain talks on a walkie talkie, then hides a tent badge.
4.The villain shines a flashlight around, then hides a tent badge.
5.The villain peers into a spy glass, then shows off a fire badge.
6.The villain shines a flashlight around, then pins on a map badge.
7.The villain throws a climbing rope, then pins on a map badge.
8.The villain looks through a decoder ring, then polishes a rope badge.
9.The villain looks through a decoder ring, then shows off a fire badge.
10.The villain peers into a spy glass, then hides a tent badge.
11.The villain talks on a walkie talkie, then pins on a map badge.
12.The villain looks through a decoder ring, then taps a star badge.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Great Treehouse Mystery
Culprit: Luke (decoder ring · star badge · righty grip · green cap · scared of frogs)
- Clue 1 (Addition): "THE VILLAIN DOES NOT HAVE THE TENT BADGE"11 + 5 = 16 (T) · 1 + 2 = 3 (N) · 7 + 4 = 11 (A) · 8 + 10 = 18 (V) · 2 + 7 = 9 (S) · 5 + 2 = 7 (O) · 4 + 11 = 15 (G) · 1 + 5 = 6 (E) · 2 + 2 = 4 (B) · 1 + 1 = 2 (I) · 4 + 6 = 10 (L) · 3 + 10 = 13 (H) · 3 + 5 = 8 (D)
- Clue 2 (Subtraction): "THEY HELD THE PEN WITH A RIGHTY GRIP"17 - 5 = 12 (T) · 9 - 3 = 6 (A) · 18 - 8 = 10 (E) · 7 - 6 = 1 (I) · 16 - 1 = 15 (P) · 11 - 2 = 9 (R) · 20 - 2 = 18 (G) · 19 - 2 = 17 (N) · 17 - 6 = 11 (D) · 15 - 8 = 7 (L) · 7 - 5 = 2 (W) · 16 - 2 = 14 (Y) · 17 - 1 = 16 (H)
- Clue 3 (Skip counting): "THEY RAN AWAY WHEN A FROG JUMPED"Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30 = 26 (T) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42 = 36 (G) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110 = 90 (M) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48 = 42 (Y) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, ___, 30, 33 = 27 (O) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, ___, 18, 20 = 16 (A) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39 = 33 (P) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120 = 100 (R) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, ___, 60, 70 = 50 (J) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65 = 55 (U) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, ___, 30, 35 = 25 (D) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, ___, 14, 16 = 12 (F) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, ___, 50, 55 = 45 (W) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150 = 130 (H) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26 = 22 (E) · Skip-count by 5s. Fill the blank: 5, 10, ___, 20, 25 = 15 (N)
- Clue 4 (Place value): "WE FOUND A GREEN CAP FIBER HERE"What number has 7 tens and 7 ones? = 77 (W) · What number has 9 tens and 3 ones? = 93 (P) · What number has 2 tens and 4 ones? = 24 (U) · What number has 6 tens and 8 ones? = 68 (O) · What number has 2 tens and 2 ones? = 22 (N) · What number has 7 tens and 3 ones? = 73 (E) · What number has 5 tens and 0 ones? = 50 (I) · What number has 4 tens and 9 ones? = 49 (H) · What number has 3 tens and 3 ones? = 33 (D) · What number has 7 tens and 0 ones? = 70 (B) · What number has 4 tens and 6 ones? = 46 (G) · What number has 9 tens and 1 one? = 91 (C) · What number has 9 tens and 5 ones? = 95 (A) · What number has 9 tens and 4 ones? = 94 (R) · What number has 1 ten and 9 ones? = 19 (F)
- Clue 5 (Missing addends): surviving statement (box 12) → Luke9 + ___ = 17 = 8 · 4 + ___ = 15 = 11 · 4 + ___ = 6 = 2 · 10 + ___ = 15 = 5 · 8 + ___ = 11 = 3 · 1 + ___ = 10 = 9 · 3 + ___ = 7 = 4 · 2 + ___ = 9 = 7 · 1 + ___ = 2 = 1 · 8 + ___ = 14 = 6 · 8 + ___ = 18 = 10
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 Great Treehouse Mystery — set in The Maple Treehouse
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects