Grade 3Reading: grades 3-4RoundingAdditionSubtractionMultiplicationDivision
The Mystery of the Missing Secret Decoder Ring
Oh no! Someone snuck into the high branches of our canopy clubhouse and snatched the legendary Gold Decoder Ring! Our team of junior detectives needs to search for clues, check the suspect list, and 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 | Club Badge | Secret Tool | Writing Hand | Cap Color | Favorite Snack |
|---|---|---|---|---|---|
| Leo | Golden Binoculars | Laser Pointer | Right-handed | Neon Blue Cap | Cheese Crackers |
| Cody | Ruby Magnifier | Walkie Talkie | Right-handed | Forest Green Cap | Apple Slices |
| Ryan | Emerald Whistle | Super Flashlight | Right-handed | Bright Red Cap | Cheese Crackers |
| Lily | Golden Binoculars | Invisible Ink | Left-handed | Bright Red Cap | Maple Popcorn |
| Ella | Bronze Key | Invisible Ink | Right-handed | Bright Red Cap | Cheese Crackers |
| Max | Ruby Magnifier | Invisible Ink | Right-handed | Bright Red Cap | Cheese Crackers |
| Ruby | Silver Compass | Invisible Ink | Right-handed | Forest Green Cap | Maple Popcorn |
| Noah | Golden Binoculars | Walkie Talkie | Right-handed | Neon Blue Cap | Cheese Crackers |
| Ben | Silver Compass | Invisible Ink | Left-handed | Bright Red Cap | Cheese Crackers |
| Emma | Ruby Magnifier | Pocket Periscope | Right-handed | Bright Red Cap | Maple Popcorn |
| Owen | Emerald Whistle | Walkie Talkie | Left-handed | Forest Green Cap | Maple Popcorn |
| Finn | Bronze Key | Super Flashlight | Right-handed | Neon Blue Cap | Cheese Crackers |
| Luke | Bronze Key | Super Flashlight | Right-handed | Neon Blue Cap | Apple Slices |
| Sam | Silver Compass | Laser Pointer | Right-handed | Bright Red Cap | Cheese Crackers |
| Jake | Golden Binoculars | Pocket Periscope | Right-handed | Bright Red Cap | Cheese Crackers |
| Mia | Emerald Whistle | Invisible Ink | Right-handed | Forest Green Cap | Apple Slices |
| Lola | Emerald Whistle | Super Flashlight | Left-handed | Forest Green Cap | Cheese Crackers |
| Maya | Golden Binoculars | Super Flashlight | Left-handed | Forest Green Cap | Maple Popcorn |
| Sofi | Silver Compass | Invisible Ink | Right-handed | Forest Green Cap | Apple Slices |
| Toby | Silver Compass | Walkie Talkie | Left-handed | Bright Red Cap | Apple Slices |
| Jack | Golden Binoculars | Invisible Ink | Left-handed | Bright Red Cap | Cheese Crackers |
Clue 1
Rounding
The radar on our spy gadget shows the suspect's escape distance, but the screen only displays numbers rounded to the nearest ten.
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
40
50
2000
5000
90
60
4000
6000
80
T
40
2000
90
700
20
2000
80
4000
20
T
40
500
80
2000
60
600
60
80
2000
90
5000
20
70
4000
T
40
2000
90
Round 37 to the nearest tenT
Round 659 to the nearest hundredD
Round 5,567 to the nearest thousandK
Round 2,046 to the nearest thousandE
Round 5,348 to the nearest thousandP
Round 60 to the nearest tenA
Round 51 to the nearest tenH
Round 67 to the nearest tenI
Round 79 to the nearest tenS
Round 615 to the nearest hundredL
Round 502 to the nearest hundredU
Round 23 to the nearest tenO
Round 91 to the nearest tenR
Round 4,098 to the nearest thousandN
0/14 letters found
Clue 2
Addition
We searched the treehouse yard and added up all the dropped magnifying glasses we found in the grass.
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
256
369
297
737
831
737
871
297
336
T
256
837
866
201
T
256
297
T
256
369
297
374
201
T
256
297
837
602
T
256
369
T
256
369
297
866
602
417
369
T
256
369
433
374
229
167 + 89 =T
526 + 340 =R
481 + 256 =S
170 + 127 =E
466 + 405 =P
212 + 157 =H
565 + 266 =U
191 + 226 =G
130 + 303 =A
87 + 114 =O
363 + 239 =I
331 + 506 =W
157 + 217 =N
176 + 160 =C
93 + 136 =D
0/15 letters found
Clue 3
Subtraction
We counted the clubhouse snack bags and subtracted the empty ones to see how many were left behind.
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
311
167
414
799
435
804
804
167
467
435
382
508
282
159
167
243
596
167
167
414
167
243
382
508
243
823
167
382
467
290
414
804
348 - 37 =W
419 - 260 =G
520 - 12 =A
364 - 197 =E
834 - 367 =D
1056 - 257 =P
473 - 183 =U
840 - 36 =T
654 - 272 =R
592 - 157 =O
1005 - 182 =K
396 - 153 =C
583 - 169 =S
937 - 341 =H
558 - 276 =N
0/15 letters found
Clue 4
Multiplication facts (1-12)
We saw rows of muddy footprints near the secret hatch and multiplied the rows to get the total count.
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
24
15
110
16
70
1
90
110
25
12
90
1
110
25
A
24
12
21
A
24
4
27
25
8
90
96
66
90
1
25
27
A
24
12
12
25
110
2 × 12 =A
2 × 4 =F
12 × 8 =O
5 × 5 =E
10 × 9 =T
10 × 11 =R
11 × 6 =N
9 × 3 =L
2 × 2 =S
2 × 8 =I
1 × 1 =H
3 × 5 =B
3 × 7 =W
10 × 7 =G
6 × 2 =D
0/15 letters found
Clue 5
Division facts (1-12) — the last clue
We split the recovered walkie talkie batteries equally among our team members to figure out the share.
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
64 ÷ 8 = ?
11 ÷ 1 = ?
50 ÷ 5 = ?
132 ÷ 11 = ?
81 ÷ 9 = ?
8 ÷ 8 = ?
30 ÷ 5 = ?
27 ÷ 9 = ?
2 ÷ 1 = ?
77 ÷ 11 = ?
10 ÷ 2 = ?
Step 2 — cross out the sentence with each answer
1.The villain shined their Ruby Magnifier on the clues, then lit up the dark room with a Super Flashlight.
2.The villain blew their Emerald Whistle to distract us, then whispered a secret code into a Walkie Talkie.
3.The villain shined their Ruby Magnifier on the clues, then peeked around the wooden corner with a Pocket Periscope.
4.The villain blew their Emerald Whistle to distract us, then lit up the dark room with a Super Flashlight.
5.The villain used their Golden Binoculars to spot the guard, then lit up the dark room with a Super Flashlight.
6.The villain turned their Bronze Key in the secret lock, then lit up the dark room with a Super Flashlight.
7.The villain shined their Ruby Magnifier on the clues, then aimed a bright green Laser Pointer.
8.The villain shined their Ruby Magnifier on the clues, then wrote a message using Invisible Ink.
9.The villain used their Golden Binoculars to spot the guard, then wrote a message using Invisible Ink.
10.The villain used their Golden Binoculars to spot the guard, then peeked around the wooden corner with a Pocket Periscope.
11.The villain turned their Bronze Key in the secret lock, then wrote a message using Invisible Ink.
12.The villain blew their Emerald Whistle to distract us, then peeked around the wooden corner with a Pocket Periscope.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Mystery of the Missing Secret Decoder Ring
Culprit: Ryan (Emerald Whistle · Super Flashlight · Right-handed · Bright Red Cap · Cheese Crackers)
- Clue 1 (Rounding): "THE PRANKSTER DOES NOT USE A LASER POINTER"Round 37 to the nearest ten = 40 (T) · Round 659 to the nearest hundred = 700 (D) · Round 5,567 to the nearest thousand = 6000 (K) · Round 2,046 to the nearest thousand = 2000 (E) · Round 5,348 to the nearest thousand = 5000 (P) · Round 60 to the nearest ten = 60 (A) · Round 51 to the nearest ten = 50 (H) · Round 67 to the nearest ten = 70 (I) · Round 79 to the nearest ten = 80 (S) · Round 615 to the nearest hundred = 600 (L) · Round 502 to the nearest hundred = 500 (U) · Round 23 to the nearest ten = 20 (O) · Round 91 to the nearest ten = 90 (R) · Round 4,098 to the nearest thousand = 4000 (N)
- Clue 2 (Addition): "THE SUSPECT WROTE THE NOTE WITH THE RIGHT HAND"167 + 89 = 256 (T) · 526 + 340 = 866 (R) · 481 + 256 = 737 (S) · 170 + 127 = 297 (E) · 466 + 405 = 871 (P) · 212 + 157 = 369 (H) · 565 + 266 = 831 (U) · 191 + 226 = 417 (G) · 130 + 303 = 433 (A) · 87 + 114 = 201 (O) · 363 + 239 = 602 (I) · 331 + 506 = 837 (W) · 157 + 217 = 374 (N) · 176 + 160 = 336 (C) · 93 + 136 = 229 (D)
- Clue 3 (Subtraction): "WE SPOTTED ORANGE CHEESE CRACKER DUST"348 - 37 = 311 (W) · 419 - 260 = 159 (G) · 520 - 12 = 508 (A) · 364 - 197 = 167 (E) · 834 - 367 = 467 (D) · 1056 - 257 = 799 (P) · 473 - 183 = 290 (U) · 840 - 36 = 804 (T) · 654 - 272 = 382 (R) · 592 - 157 = 435 (O) · 1005 - 182 = 823 (K) · 396 - 153 = 243 (C) · 583 - 169 = 414 (S) · 937 - 341 = 596 (H) · 558 - 276 = 282 (N)
- Clue 4 (Multiplication facts (1-12)): "A BRIGHT RED THREAD WAS LEFT ON THE LADDER"2 × 12 = 24 (A) · 2 × 4 = 8 (F) · 12 × 8 = 96 (O) · 5 × 5 = 25 (E) · 10 × 9 = 90 (T) · 10 × 11 = 110 (R) · 11 × 6 = 66 (N) · 9 × 3 = 27 (L) · 2 × 2 = 4 (S) · 2 × 8 = 16 (I) · 1 × 1 = 1 (H) · 3 × 5 = 15 (B) · 3 × 7 = 21 (W) · 10 × 7 = 70 (G) · 6 × 2 = 12 (D)
- Clue 5 (Division facts (1-12)): surviving statement (box 4) → Ryan64 ÷ 8 = 8 · 11 ÷ 1 = 11 · 50 ÷ 5 = 10 · 132 ÷ 11 = 12 · 81 ÷ 9 = 9 · 8 ÷ 8 = 1 · 30 ÷ 5 = 6 · 27 ÷ 9 = 3 · 2 ÷ 1 = 2 · 77 ÷ 11 = 7 · 10 ÷ 2 = 5
About this mystery
- Grade level
- Grade 3 math
- Math topics
- Rounding, Addition, Subtraction, Multiplication, Division
- Reading level
- grades 3-4
- Theme
- The Mystery of the Missing Secret Decoder Ring — set in The Secret Maple Canopy Treehouse
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects