🌊 Books, the ocean, readingGrade 5Reading: grades 7-9Fractions of a numberOrder of operationsMultiplicationRoundingDivision

The Trench Archive Heist

The waterproof vault has been breached! The legendary Abyssal Codex, containing centuries of forgotten oceanic maps, has been stolen from its pedestal. A trail of bubbles and damp footprints leads away from the scene. It is up to you to analyze the physical clues, decode the security logs, and identify which of the deep-sea researchers or submarine pilots took the precious book before they escape to the surface.

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 Marine Ability	Specialized Deep-Sea Gear	Handedness Observation	Trace Trace Evidence Found	Tactical Countermeasure
Jules Verne	Kelp Camouflage	Bioluminescent Lantern	Right-handed writing	Silver seal fur	Saltwater-dissolving nets
Yann Martel	Sonar Reading	Submersible Scooter	Right-handed writing	Sea-weed fibers	Saltwater-dissolving nets
Joseph Conrad	Deep-Sea Diving Suit	Bioluminescent Lantern	Left-handed writing	Golden mermaid hair	High-intensity flashlights
Homer	Ink-Jet Propulsion	Pressure-Proof Helmet	Right-handed writing	Silver seal fur	High-intensity flashlights
Henry Beston	Sonar Reading	Coral Harpoon	Right-handed writing	Sea-weed fibers	High-intensity flashlights
Peter Benchley	Ink-Jet Propulsion	Submersible Scooter	Right-handed writing	Golden mermaid hair	Sonic whale calls
Jacques Cousteau	Deep-Sea Diving Suit	Coral Harpoon	Right-handed writing	Sea-weed fibers	Saltwater-dissolving nets
Ishmael	Sonar Reading	Pressure-Proof Helmet	Right-handed writing	Silver seal fur	Sonic whale calls
Charles Darwin	Ink-Jet Propulsion	Pressure-Proof Helmet	Right-handed writing	Silver seal fur	Saltwater-dissolving nets
Ernest Hemingway	Deep-Sea Diving Suit	Coral Harpoon	Left-handed writing	Silver seal fur	Saltwater-dissolving nets
Clive Cussler	Kelp Camouflage	Coral Harpoon	Right-handed writing	Golden mermaid hair	Saltwater-dissolving nets
Samuel Coleridge	Ink-Jet Propulsion	Bioluminescent Lantern	Right-handed writing	Silver seal fur	Saltwater-dissolving nets
Sylvia Earle	Deep-Sea Diving Suit	Pressure-Proof Helmet	Right-handed writing	Sea-weed fibers	Saltwater-dissolving nets
Captain Nemo	Kelp Camouflage	Waterproof Tablet	Left-handed writing	Sea-weed fibers	Saltwater-dissolving nets
Ahab	Ink-Jet Propulsion	Submersible Scooter	Right-handed writing	Silver seal fur	Saltwater-dissolving nets
Rachel Carson	Ink-Jet Propulsion	Bioluminescent Lantern	Right-handed writing	Sea-weed fibers	Sonic whale calls
Herman Melville	Deep-Sea Diving Suit	Waterproof Tablet	Left-handed writing	Sea-weed fibers	Sonic whale calls
Jack London	Ink-Jet Propulsion	Waterproof Tablet	Left-handed writing	Sea-weed fibers	High-intensity flashlights
Arthur C Clarke	Sonar Reading	Waterproof Tablet	Right-handed writing	Silver seal fur	High-intensity flashlights
Mary Anning	Ink-Jet Propulsion	Waterproof Tablet	Right-handed writing	Sea-weed fibers	High-intensity flashlights
William Beebe	Deep-Sea Diving Suit	Waterproof Tablet	Right-handed writing	Silver seal fur	Saltwater-dissolving nets

Clue 1

Fractions of a number

An inventory of the archive's ledger books was partially ruined by seawater. To narrow down the suspect's gear, calculate what fraction of the ledger books remains completely dry and readable.

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

2/4 of 12 =T

8/10 of 10 =W

4/6 of 33 =L

1/4 of 104 =O

9/10 of 10 =D

1/5 of 200 =S

1/5 of 25 =E

2/8 of 116 =P

1/4 of 124 =A

1/8 of 88 =V

1/4 of 152 =F

2/10 of 135 =B

4/10 of 60 =I

1/2 of 72 =H

2/8 of 48 =N

1/6 of 198 =R

1/2 of 70 =U

0/17 letters found

Clue 2

Order of operations

The biometric security lock at the escape hatch requires entering the correct operational sequence to bypass. Solve this order of operations puzzle to unlock the footage showing which hand the thief used.

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

27 + 9 × 2 =T

12 + 5 × 2 =H

11 × 6 - 25 =N

59 + 6 × 2 =F

12 × 3 - 9 =D

12 + 5 × 7 =E

7 × 5 - 10 =L

17 + 3 × 5 =A

7 × 10 - 21 =R

6 × 12 - 18 =I

9 + 6 × 2 =P

43 + 5 × 4 =G

0/12 letters found

Clue 3

Multiplication facts (1-12)

A swarm of glowing deep-sea jellyfish was disturbed during the escape. Multiply the rows of glowing cells to determine the total energy output, which reveals the suspect's biological weakness.

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

4 × 7 =T

11 × 1 =B

4 × 12 =W

3 × 11 =P

7 × 10 =O

3 × 9 =Y

7 × 6 =L

7 × 1 =A

10 × 5 =N

7 × 8 =V

8 × 12 =H

5 × 1 =R

2 × 7 =E

12 × 6 =D

4 × 6 =S

1 × 1 =G

11 × 4 =I

0/17 letters found

Clue 4

Rounding

The submarine's automated sonar radar only displays distance measurements rounded to the nearest ten. Round these radar readings correctly to pinpoint the exact location of the hair fibers dropped during the getaway.

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

1700

110

1700

500

1300

1100

1700

110

1700

370

300

1700

500

1700

3700

1300

170

3700

300

230

1100

1700

110

3700

1700

900

230

170

4300

110

Round 90 to the nearest tenW

Round 1,136 to the nearest hundredV

Round 1,305 to the nearest hundredO

Round 32 to the nearest tenP

Round 522 to the nearest hundredC

Round 109 to the nearest tenR

Round 369 to the nearest tenD

Round 234 to the nearest tenL

Round 170 to the nearest tenF

Round 3,749 to the nearest hundredS

Round 301 to the nearest hundredI

Round 948 to the nearest hundredA

Round 1,743 to the nearest hundredE

Round 4,306 to the nearest hundredU

0/14 letters found

Clue 5

Division facts (1-12) — the last clue

To coordinate the search grid, we must share the remaining oxygen reserves equally among our recovery vessels. Divide the total liters of air to find the coordinates of the suspect's final escape vector.

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

27 ÷ 9 = ?

48 ÷ 12 = ?

108 ÷ 9 = ?

18 ÷ 9 = ?

35 ÷ 5 = ?

8 ÷ 1 = ?

63 ÷ 7 = ?

35 ÷ 7 = ?

9 ÷ 9 = ?

24 ÷ 4 = ?

70 ÷ 7 = ?

Step 2 — cross out the sentence with each answer

1.The villain employs sonar reading to scan the secret archives, then adjusts a pressure-proof helmet before escaping.

2.The villain seals their deep-sea diving suit to plunge into the abyss, then boards a submersible scooter to make a fast getaway.

3.The villain uses ink-jet propulsion to glide through the shelves, then swings a bioluminescent lantern to read in the dark.

4.The villain uses ink-jet propulsion to glide through the shelves, then boards a submersible scooter to make a fast getaway.

5.The villain seals their deep-sea diving suit to plunge into the abyss, then adjusts a pressure-proof helmet before escaping.

6.The villain employs sonar reading to scan the secret archives, then taps a waterproof tablet to log the stolen data.

7.The villain activates kelp camouflage to blend into the ocean walls, then taps a waterproof tablet to log the stolen data.

8.The villain employs sonar reading to scan the secret archives, then brandishes a coral harpoon to keep the guards back.

9.The villain uses ink-jet propulsion to glide through the shelves, then brandishes a coral harpoon to keep the guards back.

10.The villain activates kelp camouflage to blend into the ocean walls, then boards a submersible scooter to make a fast getaway.

11.The villain activates kelp camouflage to blend into the ocean walls, then swings a bioluminescent lantern to read in the dark.

12.The villain uses ink-jet propulsion to glide through the shelves, then adjusts a pressure-proof helmet before escaping.

Solve it

Name the culprit

Choose the one suspect left standing.

Answer Key — The Trench Archive Heist

Culprit: Jules Verne (Kelp Camouflage · Bioluminescent Lantern · Right-handed writing · Silver seal fur · Saltwater-dissolving nets)

Clue 1 (Fractions of a number): "THE VILLAIN DOES NOT USE A WATERPROOF TABLET"
2/4 of 12 = 6 (T) · 8/10 of 10 = 8 (W) · 4/6 of 33 = 22 (L) · 1/4 of 104 = 26 (O) · 9/10 of 10 = 9 (D) · 1/5 of 200 = 40 (S) · 1/5 of 25 = 5 (E) · 2/8 of 116 = 29 (P) · 1/4 of 124 = 31 (A) · 1/8 of 88 = 11 (V) · 1/4 of 152 = 38 (F) · 2/10 of 135 = 27 (B) · 4/10 of 60 = 24 (I) · 1/2 of 72 = 36 (H) · 2/8 of 48 = 12 (N) · 1/6 of 198 = 33 (R) · 1/2 of 70 = 35 (U)
Clue 2 (Order of operations): "THE THIEF HELD THE PEN IN THEIR RIGHT HAND"
27 + 9 × 2 = 45 (T) · 12 + 5 × 2 = 22 (H) · 11 × 6 - 25 = 41 (N) · 59 + 6 × 2 = 71 (F) · 12 × 3 - 9 = 27 (D) · 12 + 5 × 7 = 47 (E) · 7 × 5 - 10 = 25 (L) · 17 + 3 × 5 = 32 (A) · 7 × 10 - 21 = 49 (R) · 6 × 12 - 18 = 54 (I) · 9 + 6 × 2 = 21 (P) · 43 + 5 × 4 = 63 (G)
Clue 3 (Multiplication facts (1-12)): "THE VILLAIN WAS TRAPPED BY DISSOLVING NETS"
4 × 7 = 28 (T) · 11 × 1 = 11 (B) · 4 × 12 = 48 (W) · 3 × 11 = 33 (P) · 7 × 10 = 70 (O) · 3 × 9 = 27 (Y) · 7 × 6 = 42 (L) · 7 × 1 = 7 (A) · 10 × 5 = 50 (N) · 7 × 8 = 56 (V) · 8 × 12 = 96 (H) · 5 × 1 = 5 (R) · 2 × 7 = 14 (E) · 12 × 6 = 72 (D) · 4 × 6 = 24 (S) · 1 × 1 = 1 (G) · 11 × 4 = 44 (I)
Clue 4 (Rounding): "WE RECOVERED PIECES OF SILVER SEAL FUR"
Round 90 to the nearest ten = 90 (W) · Round 1,136 to the nearest hundred = 1100 (V) · Round 1,305 to the nearest hundred = 1300 (O) · Round 32 to the nearest ten = 30 (P) · Round 522 to the nearest hundred = 500 (C) · Round 109 to the nearest ten = 110 (R) · Round 369 to the nearest ten = 370 (D) · Round 234 to the nearest ten = 230 (L) · Round 170 to the nearest ten = 170 (F) · Round 3,749 to the nearest hundred = 3700 (S) · Round 301 to the nearest hundred = 300 (I) · Round 948 to the nearest hundred = 900 (A) · Round 1,743 to the nearest hundred = 1700 (E) · Round 4,306 to the nearest hundred = 4300 (U)
Clue 5 (Division facts (1-12)): surviving statement (box 11) → Jules Verne
27 ÷ 9 = 3 · 48 ÷ 12 = 4 · 108 ÷ 9 = 12 · 18 ÷ 9 = 2 · 35 ÷ 5 = 7 · 8 ÷ 1 = 8 · 63 ÷ 7 = 9 · 35 ÷ 7 = 5 · 9 ÷ 9 = 1 · 24 ÷ 4 = 6 · 70 ÷ 7 = 10

About this mystery

Grade level: Grade 5 math
Math topics: Fractions of a number, Order of operations, Multiplication, Rounding, Division
Reading level: grades 7-9
Theme: The Trench Archive Heist — set in The Abyssal Library, a pressurized glass dome anchored at the bottom of the Mariana Trench
Format: Interactive online & printable worksheet with answer key
Solution: One unique, verified culprit among 21 suspects

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