🤖 Robots, MermaidsGrade 2Reading: grades 1-2Place valueAdditionSubtractionSkip countingMissing addends
The Rustreef Reef Mystery
Oh no! The golden Pearl of Rustreef is gone. A bad robo-mermaid took it from the Reef Mayor. Detective Diver must follow the clues and find them!
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 | Main Power | Extra Tool | Dominant Hand | Hair Material | System Weakness |
|---|---|---|---|---|---|
| Turbine | laser tail | rust beam | left handed | pink kelp | sand spray |
| Sparky | laser tail | oil slick | left handed | gold foil | sand spray |
| Widget | laser tail | rust beam | right handed | pink kelp | magnet wand |
| Sprocket | metal claw | rust beam | left handed | gold foil | fresh water |
| Rusty | bubble shield | oil slick | right handed | gold foil | fresh water |
| Shelly | metal claw | net launcher | left handed | gold foil | fresh water |
| Beep | turbo fin | scrap magnet | left handed | gold foil | fresh water |
| Waverly | sonar song | spark shock | left handed | gold foil | fresh water |
| Coral | bubble shield | scrap magnet | left handed | pink kelp | fresh water |
| Cog | bubble shield | oil slick | right handed | pink kelp | fresh water |
| Gasket | turbo fin | oil slick | right handed | gold foil | magnet wand |
| Finley | metal claw | oil slick | left handed | gold foil | magnet wand |
| Melody | laser tail | net launcher | left handed | gold foil | fresh water |
| Marina | metal claw | scrap magnet | left handed | neon wire | fresh water |
| Splash | sonar song | rust beam | left handed | gold foil | fresh water |
| Circuit | sonar song | rust beam | right handed | neon wire | sand spray |
| Bolt | turbo fin | spark shock | right handed | neon wire | fresh water |
| Ariel | turbo fin | spark shock | left handed | pink kelp | magnet wand |
| Dynamo | bubble shield | spark shock | right handed | neon wire | sand spray |
| Sandy | sonar song | rust beam | left handed | neon wire | sand spray |
| Chip | bubble shield | scrap magnet | right handed | gold foil | magnet wand |
Clue 1
Place value
We look at the escape pod screen. It shows the speed using ones and tens.
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
44
15
85
26
30
28
28
22
30
61
55
53
85
70
61
53
T
44
83
70
85
T
44
15
85
99
83
70
T
44
49
85
22
40
What number has 4 tens and 4 ones?T
What number has 7 tens and 0 ones?S
What number has 5 tens and 5 ones?D
What number has 2 tens and 6 ones?V
What number has 8 tens and 5 ones?E
What number has 9 tens and 9 ones?R
What number has 2 tens and 8 ones?L
What number has 1 ten and 5 ones?H
What number has 4 tens and 0 ones?M
What number has 2 tens and 2 ones?A
What number has 8 tens and 3 ones?U
What number has 6 tens and 1 one?N
What number has 4 tens and 9 ones?B
What number has 5 tens and 3 ones?O
What number has 3 tens and 0 ones?I
0/15 letters found
Clue 2
Addition
We count the shiny power gears found on the sandy floor to find the 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
25
60
57
33
65
94
94
92
40
78
57
43
T
25
60
57
44
65
63
57
66
T
25
60
69
29
43
14 + 11 =T
22 + 44 =F
10 + 19 =N
18 + 42 =H
28 + 41 =A
14 + 26 =U
16 + 28 =I
29 + 63 =K
31 + 47 =S
40 + 17 =E
18 + 15 =C
24 + 39 =L
24 + 41 =R
17 + 26 =D
53 + 41 =O
0/15 letters found
Clue 3
Subtraction
Our mini submarine had ten batteries. The villain took some away.
Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.
F
33
52
64
38
54
67
63
50
64
52
66
63
86
64
38
50
54
64
66
57
47
55
50
65
54
42 - 9 =F
106 - 20 =K
84 - 30 =H
48 - 10 =S
83 - 31 =R
73 - 16 =G
100 - 34 =M
85 - 22 =A
73 - 9 =E
81 - 16 =C
78 - 23 =I
74 - 27 =L
84 - 17 =W
51 - 1 =T
0/14 letters found
Clue 4
Skip counting
The bad bot left a trail of glowing pearls. They are grouped in twos.
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
21
36
24
45
60
42
27
12
45
35
27
24
45
28
35
33
70
70
30
36
130
110
36
42
36
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, ___, 24, 27W
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42E
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, ___, 65, 70U
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, ___, 14, 16G
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32I
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, ___, 80, 90T
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, ___, 27, 30F
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, ___, 120, 130C
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150S
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48N
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, ___, 35, 40H
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, ___, 40, 45L
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, ___, 30, 33D
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, ___, 50, 55O
0/15 letters found
Clue 5
Missing addends — the last clue
The sea vault needs eight power cards. We only have five so far.
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
7 + ___ = 15
9 + ___ = 18
10 + ___ = 21
2 + ___ = 8
10 + ___ = 20
10 + ___ = 14
6 + ___ = 13
5 + ___ = 6
9 + ___ = 11
8 + ___ = 11
7 + ___ = 12
Step 2 — cross out the sentence with each answer
1.The villain sings a loud sonar song, then pulls some heavy scrap metal.
2.The villain grabs things with a metal claw, then shocks a clam with a spark.
3.The villain creates a giant bubble shield, then fires a hot rust beam.
4.The villain flashes a bright laser tail, then shocks a clam with a spark.
5.The villain grabs things with a metal claw, then pulls some heavy scrap metal.
6.The villain creates a giant bubble shield, then shoots a sticky net launcher.
7.The villain flashes a bright laser tail, then pulls some heavy scrap metal.
8.The villain sings a loud sonar song, then shocks a clam with a spark.
9.The villain flashes a bright laser tail, then shoots a sticky net launcher.
10.The villain sings a loud sonar song, then shoots a sticky net launcher.
11.The villain jets away with a turbo fin, then pulls some heavy scrap metal.
12.The villain grabs things with a metal claw, then shoots a sticky net launcher.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Rustreef Reef Mystery
Culprit: Shelly (metal claw · net launcher · left handed · gold foil · fresh water)
- Clue 1 (Place value): "THE VILLAIN DOES NOT USE THE RUST BEAM"What number has 4 tens and 4 ones? = 44 (T) · What number has 7 tens and 0 ones? = 70 (S) · What number has 5 tens and 5 ones? = 55 (D) · What number has 2 tens and 6 ones? = 26 (V) · What number has 8 tens and 5 ones? = 85 (E) · What number has 9 tens and 9 ones? = 99 (R) · What number has 2 tens and 8 ones? = 28 (L) · What number has 1 ten and 5 ones? = 15 (H) · What number has 4 tens and 0 ones? = 40 (M) · What number has 2 tens and 2 ones? = 22 (A) · What number has 8 tens and 3 ones? = 83 (U) · What number has 6 tens and 1 one? = 61 (N) · What number has 4 tens and 9 ones? = 49 (B) · What number has 5 tens and 3 ones? = 53 (O) · What number has 3 tens and 0 ones? = 30 (I)
- Clue 2 (Addition): "THE CROOK USED THEIR LEFT HAND"14 + 11 = 25 (T) · 22 + 44 = 66 (F) · 10 + 19 = 29 (N) · 18 + 42 = 60 (H) · 28 + 41 = 69 (A) · 14 + 26 = 40 (U) · 16 + 28 = 44 (I) · 29 + 63 = 92 (K) · 31 + 47 = 78 (S) · 40 + 17 = 57 (E) · 18 + 15 = 33 (C) · 24 + 39 = 63 (L) · 24 + 41 = 65 (R) · 17 + 26 = 43 (D) · 53 + 41 = 94 (O)
- Clue 3 (Subtraction): "FRESH WATER MAKES THEM GLITCH"42 - 9 = 33 (F) · 106 - 20 = 86 (K) · 84 - 30 = 54 (H) · 48 - 10 = 38 (S) · 83 - 31 = 52 (R) · 73 - 16 = 57 (G) · 100 - 34 = 66 (M) · 85 - 22 = 63 (A) · 73 - 9 = 64 (E) · 81 - 16 = 65 (C) · 78 - 23 = 55 (I) · 74 - 27 = 47 (L) · 84 - 17 = 67 (W) · 51 - 1 = 50 (T)
- Clue 4 (Skip counting): "WE FOUND GOLD FOIL AT THE SCENE"Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, ___, 24, 27 = 21 (W) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, ___, 39, 42 = 36 (E) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, ___, 65, 70 = 60 (U) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, ___, 14, 16 = 12 (G) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32 = 28 (I) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, ___, 80, 90 = 70 (T) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, ___, 27, 30 = 24 (F) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, ___, 120, 130 = 110 (C) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150 = 130 (S) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48 = 42 (N) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, ___, 35, 40 = 30 (H) · 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, ___, 40, 45 = 35 (L) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, ___, 30, 33 = 27 (D) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, ___, 50, 55 = 45 (O)
- Clue 5 (Missing addends): surviving statement (box 12) → Shelly7 + ___ = 15 = 8 · 9 + ___ = 18 = 9 · 10 + ___ = 21 = 11 · 2 + ___ = 8 = 6 · 10 + ___ = 20 = 10 · 10 + ___ = 14 = 4 · 6 + ___ = 13 = 7 · 5 + ___ = 6 = 1 · 9 + ___ = 11 = 2 · 8 + ___ = 11 = 3 · 7 + ___ = 12 = 5
About this mystery
- Grade level
- Grade 2 math
- Math topics
- Place value, Addition, Subtraction, Skip counting, Missing addends
- Reading level
- grades 1-2
- Theme
- The Rustreef Reef Mystery — set in Rustreef Cove, a glowing underwater dome for robot mermaids
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects