🔎 DetectivesGrade 3Reading: grades 3-4Place valueAdditionSubtractionMultiplicationMissing addends

The Case of the Missing Diamond

A master rogue called the Shadow Thief sneaked into the museum and stole the famous Star Diamond. Chief Detective Miller needs your help analyzing clues left at the scene to catch the right suspect.

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	Primary Skill	Favorite Tool	Dominant Hand	Hair Color	Major Weakness
Perry Mason	Code Breaking	Magnifying Glass	Right Handed	Black Hair	Barking Dogs
Amelia Peabody	Code Breaking	Magnifying Glass	Left Handed	Red Hair	Loud Sirens
Phryne Fisher	Stealth Walking	Magnifying Glass	Left Handed	Red Hair	Barking Dogs
Nancy Drew	Vault Cracking	Disguise Mask	Right Handed	Red Hair	Barking Dogs
Cormoran Strike	Code Breaking	Invisible Ink	Left Handed	Black Hair	Barking Dogs
Joe Hardy	Stealth Walking	Disguise Mask	Left Handed	Red Hair	Loud Sirens
Velma Dinkley	Code Breaking	Magnifying Glass	Left Handed	Red Hair	Barking Dogs
Cam Jansen	Code Breaking	Invisible Ink	Left Handed	Blonde Hair	Barking Dogs
Frank Hardy	Code Breaking	Magnifying Glass	Right Handed	Blonde Hair	Barking Dogs
Ellery Queen	Lock Picking	Invisible Ink	Left Handed	Blonde Hair	Loud Sirens
Encyclopedia Brown	Code Breaking	Invisible Ink	Right Handed	Black Hair	Barking Dogs
Sam Spade	Code Breaking	Smoke Bombs	Right Handed	Black Hair	Loud Sirens
Veronica Mars	Stealth Walking	Handy Lockpicks	Left Handed	Black Hair	Barking Dogs
Miss Marple	Vault Cracking	Handy Lockpicks	Right Handed	Black Hair	Loud Sirens
Enola Holmes	Code Breaking	Magnifying Glass	Right Handed	Blonde Hair	Loud Sirens
C Auguste Dupin	Vault Cracking	Handy Lockpicks	Left Handed	Black Hair	Flashing Lights
Detective Conan	Vault Cracking	Smoke Bombs	Right Handed	Black Hair	Barking Dogs
Inspector Clouseau	Lock Picking	Disguise Mask	Right Handed	Red Hair	Barking Dogs
Nero Wolfe	Lock Picking	Disguise Mask	Right Handed	Black Hair	Barking Dogs
Dick Tracy	Stealth Walking	Handy Lockpicks	Right Handed	Blonde Hair	Flashing Lights
Philip Marlowe	Shadow Disguise	Handy Lockpicks	Right Handed	Black Hair	Barking Dogs

Clue 1

Place value

Inspect the digital badge display at the museum entrance. Check the digit in the tens place to decode this report.

Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.

400

8000

300

2000

4000

900

300

4000

300

700

600

300

6000

800

300

1000

800

6000

1000

What is the value of the 4 in 460?T

What is the value of the 8 in 870?O

What is the value of the 3 in 354?E

What is the value of the 1 in 1,567?B

What is the value of the 6 in 4,362?N

What is the value of the 6 in 36,784?M

What is the value of the 5 in 7,459?L

What is the value of the 2 in 725?A

What is the value of the 4 in 74,275?V

What is the value of the 7 in 728?R

What is the value of the 9 in 4,903?I

What is the value of the 2 in 2,179?Y

What is the value of the 6 in 623?U

What is the value of the 8 in 1,387?S

What is the value of the 8 in 8,694?H

What is the value of the 9 in 6,098?K

0/16 letters found

Clue 2

Addition

Add up all the footprint evidence tokens found in the hallway to reveal this suspect report.

Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.

582

465

550

911

850

645

693

550

541

540

465

376

726

541

550

850

465

693

352

850

645

352

540

550

540

726

693

707

266 + 316 =F

201 + 349 =T

273 + 577 =R

289 + 437 =A

347 + 346 =N

194 + 346 =H

432 + 213 =I

254 + 122 =W

198 + 154 =G

305 + 160 =O

431 + 480 =P

341 + 200 =S

478 + 229 =D

0/13 letters found

Clue 3

Subtraction

Subtract the damaged evidence files from the master stack to unlock this detective 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.

280

821

564

285

282

564

172

553

160

280

821

737

564

125

410

172

285

229

172

164

564

641

262

160

262

172

164

553

737

282

505

641

261

505

285

451 - 171 =T

519 - 394 =F

882 - 329 =K

477 - 195 =N

484 - 320 =R

809 - 168 =D

334 - 49 =S

715 - 305 =W

584 - 323 =O

917 - 180 =I

505 - 243 =B

601 - 372 =C

515 - 355 =Y

864 - 359 =G

558 - 386 =A

870 - 49 =H

802 - 238 =E

0/17 letters found

Clue 4

Multiplication facts (1-12)

Multiply the rows of fingerprint cards in the filing cabinet to solve 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.

120

110

132

11 × 6 =A

12 × 7 =F

7 × 4 =D

9 × 1 =C

10 × 7 =S

10 × 11 =N

8 × 12 =L

2 × 7 =O

7 × 8 =T

9 × 7 =H

11 × 2 =E

7 × 5 =U

8 × 11 =B

12 × 10 =I

10 × 5 =K

12 × 11 =V

3 × 6 =R

6 × 12 =W

0/18 letters found

Clue 5

Missing addends — the last clue

Find the missing number of clue badges needed to complete the case board.

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 + ___ = 7

9 + ___ = 18

3 + ___ = 14

8 + ___ = 18

8 + ___ = 12

10 + ___ = 17

2 + ___ = 5

6 + ___ = 18

5 + ___ = 13

9 + ___ = 15

4 + ___ = 9

Step 2 — cross out the sentence with each answer

1.The villain breaks the secret security code, then searches with a magnifying glass.

2.The villain breaks the secret security code, then writes notes in invisible ink.

3.The villain picks the heavy metal lock, then writes notes in invisible ink.

4.The villain breaks the secret security code, then uses handy lockpicks.

5.The villain uses a shadow disguise, then drops a cloud of smoke bombs.

6.The villain cracks the high tech vault, then searches with a magnifying glass.

7.The villain uses a shadow disguise, then writes notes in invisible ink.

8.The villain walks softly without a sound, then writes notes in invisible ink.

9.The villain uses a shadow disguise, then uses handy lockpicks.

10.The villain picks the heavy metal lock, then searches with a magnifying glass.

11.The villain picks the heavy metal lock, then puts on a quick disguise mask.

12.The villain cracks the high tech vault, then puts on a quick disguise mask.

Solve it

Name the culprit

Choose the one suspect left standing.

Answer Key — The Case of the Missing Diamond

Culprit: Perry Mason (Code Breaking · Magnifying Glass · Right Handed · Black Hair · Barking Dogs)

Clue 1 (Place value): "THE SNEAKY VILLAIN NEVER USES SMOKE BOMBS"
What is the value of the 4 in 460? = 400 (T) · What is the value of the 8 in 870? = 800 (O) · What is the value of the 3 in 354? = 300 (E) · What is the value of the 1 in 1,567? = 1000 (B) · What is the value of the 6 in 4,362? = 60 (N) · What is the value of the 6 in 36,784? = 6000 (M) · What is the value of the 5 in 7,459? = 50 (L) · What is the value of the 2 in 725? = 20 (A) · What is the value of the 4 in 74,275? = 4000 (V) · What is the value of the 7 in 728? = 700 (R) · What is the value of the 9 in 4,903? = 900 (I) · What is the value of the 2 in 2,179? = 2000 (Y) · What is the value of the 6 in 623? = 600 (U) · What is the value of the 8 in 1,387? = 80 (S) · What is the value of the 8 in 8,694? = 8000 (H) · What is the value of the 9 in 6,098? = 90 (K)
Clue 2 (Addition): "FOOTPRINTS SHOW A STRONG RIGHT HAND"
266 + 316 = 582 (F) · 201 + 349 = 550 (T) · 273 + 577 = 850 (R) · 289 + 437 = 726 (A) · 347 + 346 = 693 (N) · 194 + 346 = 540 (H) · 432 + 213 = 645 (I) · 254 + 122 = 376 (W) · 198 + 154 = 352 (G) · 305 + 160 = 465 (O) · 431 + 480 = 911 (P) · 341 + 200 = 541 (S) · 478 + 229 = 707 (D)
Clue 3 (Subtraction): "THE SNEAKY THIEF WAS SCARED BY BARKING DOGS"
451 - 171 = 280 (T) · 519 - 394 = 125 (F) · 882 - 329 = 553 (K) · 477 - 195 = 282 (N) · 484 - 320 = 164 (R) · 809 - 168 = 641 (D) · 334 - 49 = 285 (S) · 715 - 305 = 410 (W) · 584 - 323 = 261 (O) · 917 - 180 = 737 (I) · 505 - 243 = 262 (B) · 601 - 372 = 229 (C) · 515 - 355 = 160 (Y) · 864 - 359 = 505 (G) · 558 - 386 = 172 (A) · 870 - 49 = 821 (H) · 802 - 238 = 564 (E)
Clue 4 (Multiplication facts (1-12)): "A BLACK HAIR WAS FOUND ON THE VAULT LOCK"
11 × 6 = 66 (A) · 12 × 7 = 84 (F) · 7 × 4 = 28 (D) · 9 × 1 = 9 (C) · 10 × 7 = 70 (S) · 10 × 11 = 110 (N) · 8 × 12 = 96 (L) · 2 × 7 = 14 (O) · 7 × 8 = 56 (T) · 9 × 7 = 63 (H) · 11 × 2 = 22 (E) · 7 × 5 = 35 (U) · 8 × 11 = 88 (B) · 12 × 10 = 120 (I) · 10 × 5 = 50 (K) · 12 × 11 = 132 (V) · 3 × 6 = 18 (R) · 6 × 12 = 72 (W)
Clue 5 (Missing addends): surviving statement (box 1) → Perry Mason
5 + ___ = 7 = 2 · 9 + ___ = 18 = 9 · 3 + ___ = 14 = 11 · 8 + ___ = 18 = 10 · 8 + ___ = 12 = 4 · 10 + ___ = 17 = 7 · 2 + ___ = 5 = 3 · 6 + ___ = 18 = 12 · 5 + ___ = 13 = 8 · 9 + ___ = 15 = 6 · 4 + ___ = 9 = 5

About this mystery

Grade level: Grade 3 math
Math topics: Place value, Addition, Subtraction, Multiplication, Missing addends
Reading level: grades 3-4
Theme: The Case of the Missing Diamond — set in Metro City Detective Headquarters
Format: Interactive online & printable worksheet with answer key
Solution: One unique, verified culprit among 21 suspects

More free printable math cases

3rd grade worksheets Addition worksheets Subtraction worksheets Multiplication worksheets Place value worksheets Missing addends worksheets All worksheets →

The Mystery of the Rainbow Reef Trophy

Grade 3

The Mystery of the Missing Golden Trophy

Grade 3

The Mystery of the Missing Golden Trophy

Grade 3

Mystery of the Cloud Island Map

Grade 3