🌊 Cats, MermaidsGrade 1Reading: grades 1-2Place valueAdditionSubtractionSkip countingMissing addends
The Case of the Golden Shell
A sneaky cat-mermaid took the Golden Shell from the Royal Fish Keeper! Use your math skills to help the Purr-maids find the thief.
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 | Magic Power | Favorite Toy | Paw Preference | Tail Fur Color | Secret Fear |
|---|---|---|---|---|---|
| Mimi | shell shield | shiny bell | right paw writer | black tail fur | loud dog barks |
| Finny | shell shield | laser toy | right paw writer | orange tail fur | loud dog barks |
| Pearl | kelp lasso | shiny bell | left paw writer | black tail fur | bright lights |
| Tailer | pearl blast | catnip mouse | right paw writer | orange tail fur | squirting water |
| Toby | pearl blast | laser toy | right paw writer | black tail fur | loud dog barks |
| Fluffy | coral dash | yarn ball | left paw writer | white tail fur | squirting water |
| Patch | pearl blast | feather wand | left paw writer | black tail fur | bright lights |
| Barnaby | bubble magic | catnip mouse | right paw writer | orange tail fur | loud dog barks |
| Ocean | bubble magic | catnip mouse | right paw writer | black tail fur | loud dog barks |
| Mittens | bubble magic | laser toy | right paw writer | black tail fur | squirting water |
| Kiwi | kelp lasso | catnip mouse | left paw writer | black tail fur | loud dog barks |
| Shelly | kelp lasso | yarn ball | right paw writer | black tail fur | bright lights |
| Whiskers | kelp lasso | yarn ball | right paw writer | orange tail fur | loud dog barks |
| Coral | pearl blast | yarn ball | right paw writer | black tail fur | loud dog barks |
| Sandy | coral dash | laser toy | right paw writer | white tail fur | squirting water |
| Bubbles | pearl blast | yarn ball | left paw writer | black tail fur | bright lights |
| Pip | coral dash | shiny bell | right paw writer | black tail fur | bright lights |
| Marina | shell shield | shiny bell | right paw writer | white tail fur | bright lights |
| Salty | coral dash | shiny bell | left paw writer | white tail fur | squirting water |
| Slick | kelp lasso | feather wand | right paw writer | black tail fur | loud dog barks |
| Paws | shell shield | catnip mouse | right paw writer | orange tail fur | squirting water |
Clue 1
Place value
Look at this seashell chart. The digits tell us the secret room number. This clue helps us find the thief.
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
87
72
21
T
87
72
78
21
52
40
22
21
63
64
22
T
87
72
68
17
21
68
63
72
78
64
61
39
21
54
54
What number has 8 tens and 7 ones?T
What number has 2 tens and 1 one?E
What number has 2 tens and 2 ones?O
What number has 6 tens and 3 ones?S
What number has 6 tens and 1 one?Y
What number has 3 tens and 9 ones?B
What number has 1 ten and 7 ones?V
What number has 6 tens and 4 ones?N
What number has 4 tens and 0 ones?D
What number has 7 tens and 2 ones?H
What number has 5 tens and 4 ones?L
What number has 7 tens and 8 ones?I
What number has 6 tens and 8 ones?A
What number has 5 tens and 2 ones?F
0/14 letters found
Clue 2
Addition
Let us add up the shiny pearls we found in the sand. When we count them all together, we get a new 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
20
17
4
T
20
17
9
4
2
17
4
16
3
T
20
17
4
13
8
19
18
6
7
9
7
T
20
17
4
9
8
8
9
11
17
T
20
14
19
10
11 + 9 =T
8 + 11 =A
8 + 3 =G
4 + 6 =W
9 + 5 =P
6 + 3 =I
5 + 3 =R
12 + 6 =Y
2 + 4 =O
5 + 2 =N
7 + 10 =H
10 + 3 =C
10 + 6 =L
2 + 1 =D
2 + 2 =E
1 + 1 =F
0/16 letters found
Clue 3
Subtraction
The thief dropped some starfish. If we take away the broken ones, we will see a hidden clue on the sand.
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
1
18
T
10
1
16
18
17
14
13
2
13
9
13
8
17
14
5
3
19
5
4
12
12
5
6
7
13
14
11
15
15 - 5 =T
19 - 5 =R
8 - 2 =G
19 - 2 =F
14 - 2 =D
17 - 8 =W
7 - 4 =M
9 - 1 =Y
8 - 1 =B
20 - 4 =I
6 - 5 =H
20 - 7 =A
11 - 9 =N
8 - 4 =U
16 - 5 =K
20 - 1 =L
19 - 1 =E
11 - 6 =O
16 - 1 =S
0/19 letters found
Clue 4
Skip counting
Follow the paw prints! Count them by twos to reach the end of the path and find this 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.
W
42
22
6
65
24
33
40
20
10
100
60
8
6
24
130
65
33
36
18
22
140
65
10
40
22
33
28
18
22
10
10
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48W
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, ___, 27, 30U
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, ___, 65, 70C
Skip-count by 2s. Fill the blank: 2, 4, ___, 8, 10F
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150R
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26E
Skip-count by 10s. Fill the blank: 10, 20, 30, ___, 50, 60D
Skip-count by 5s. Fill the blank: 5, 10, 15, ___, 25, 30B
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75O
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32S
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39N
Skip-count by 2s. Fill the blank: 2, 4, 6, ___, 10, 12K
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, ___, 21, 24H
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, ___, 150, 160G
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, ___, 12, 14L
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42T
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120A
0/17 letters found
Clue 5
Missing addends — the last clue
We need ten shiny rocks to open the treasure box. We only have six. Solve for the missing number to get the final clue.
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
5 + ___ = 16
1 + ___ = 8
6 + ___ = 12
2 + ___ = 12
6 + ___ = 11
1 + ___ = 5
9 + ___ = 17
8 + ___ = 17
9 + ___ = 10
4 + ___ = 6
2 + ___ = 5
Step 2 — cross out the sentence with each answer
1.The villain blocked the guard with a shell shield, then shined a red laser toy on the floor.
2.The villain dashed through the coral reef, then waved a feather wand in the air.
3.The villain blocked the guard with a shell shield, then dropped a big green yarn ball.
4.The villain threw a kelp lasso to grab the treasure, then shined a red laser toy on the floor.
5.The villain shot a blast of pearls to distract everyone, then rang a shiny bell to celebrate.
6.The villain threw a kelp lasso to grab the treasure, then waved a feather wand in the air.
7.The villain blew big bubbles to block the path, then tossed a catnip mouse into the weeds.
8.The villain threw a kelp lasso to grab the treasure, then tossed a catnip mouse into the weeds.
9.The villain dashed through the coral reef, then dropped a big green yarn ball.
10.The villain shot a blast of pearls to distract everyone, then waved a feather wand in the air.
11.The villain shot a blast of pearls to distract everyone, then shined a red laser toy on the floor.
12.The villain shot a blast of pearls to distract everyone, then dropped a big green yarn ball.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Case of the Golden Shell
Culprit: Coral (pearl blast · yarn ball · right paw writer · black tail fur · loud dog barks)
- Clue 1 (Place value): "THE THIEF DOES NOT HAVE A SHINY BELL"What number has 8 tens and 7 ones? = 87 (T) · What number has 2 tens and 1 one? = 21 (E) · What number has 2 tens and 2 ones? = 22 (O) · What number has 6 tens and 3 ones? = 63 (S) · What number has 6 tens and 1 one? = 61 (Y) · What number has 3 tens and 9 ones? = 39 (B) · What number has 1 ten and 7 ones? = 17 (V) · What number has 6 tens and 4 ones? = 64 (N) · What number has 4 tens and 0 ones? = 40 (D) · What number has 7 tens and 2 ones? = 72 (H) · What number has 5 tens and 4 ones? = 54 (L) · What number has 7 tens and 8 ones? = 78 (I) · What number has 6 tens and 8 ones? = 68 (A) · What number has 5 tens and 2 ones? = 52 (F)
- Clue 2 (Addition): "THE THIEF HELD THE CRAYON IN THEIR RIGHT PAW"11 + 9 = 20 (T) · 8 + 11 = 19 (A) · 8 + 3 = 11 (G) · 4 + 6 = 10 (W) · 9 + 5 = 14 (P) · 6 + 3 = 9 (I) · 5 + 3 = 8 (R) · 12 + 6 = 18 (Y) · 2 + 4 = 6 (O) · 5 + 2 = 7 (N) · 7 + 10 = 17 (H) · 10 + 3 = 13 (C) · 10 + 6 = 16 (L) · 2 + 1 = 3 (D) · 2 + 2 = 4 (E) · 1 + 1 = 2 (F)
- Clue 3 (Subtraction): "THE THIEF RAN AWAY FROM LOUD DOG BARKS"15 - 5 = 10 (T) · 19 - 5 = 14 (R) · 8 - 2 = 6 (G) · 19 - 2 = 17 (F) · 14 - 2 = 12 (D) · 17 - 8 = 9 (W) · 7 - 4 = 3 (M) · 9 - 1 = 8 (Y) · 8 - 1 = 7 (B) · 20 - 4 = 16 (I) · 6 - 5 = 1 (H) · 20 - 7 = 13 (A) · 11 - 9 = 2 (N) · 8 - 4 = 4 (U) · 16 - 5 = 11 (K) · 20 - 1 = 19 (L) · 19 - 1 = 18 (E) · 11 - 6 = 5 (O) · 16 - 1 = 15 (S)
- Clue 4 (Skip counting): "WE FOUND BLACK FUR ON THE GOLDEN SHELL"Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48 = 42 (W) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, ___, 27, 30 = 24 (U) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, ___, 65, 70 = 60 (C) · Skip-count by 2s. Fill the blank: 2, 4, ___, 8, 10 = 6 (F) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150 = 130 (R) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26 = 22 (E) · Skip-count by 10s. Fill the blank: 10, 20, 30, ___, 50, 60 = 40 (D) · Skip-count by 5s. Fill the blank: 5, 10, 15, ___, 25, 30 = 20 (B) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75 = 65 (O) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32 = 28 (S) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39 = 33 (N) · Skip-count by 2s. Fill the blank: 2, 4, 6, ___, 10, 12 = 8 (K) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, ___, 21, 24 = 18 (H) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, ___, 150, 160 = 140 (G) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, ___, 12, 14 = 10 (L) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42 = 36 (T) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120 = 100 (A)
- Clue 5 (Missing addends): surviving statement (box 12) → Coral5 + ___ = 16 = 11 · 1 + ___ = 8 = 7 · 6 + ___ = 12 = 6 · 2 + ___ = 12 = 10 · 6 + ___ = 11 = 5 · 1 + ___ = 5 = 4 · 9 + ___ = 17 = 8 · 8 + ___ = 17 = 9 · 9 + ___ = 10 = 1 · 4 + ___ = 6 = 2 · 2 + ___ = 5 = 3
About this mystery
- Grade level
- Grade 1 math
- Math topics
- Place value, Addition, Subtraction, Skip counting, Missing addends
- Reading level
- grades 1-2
- Theme
- The Case of the Golden Shell — set in The Sparkle Coral Reef
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects