Grade 4Reading: grades 3-4Place valueAdditionSubtractionRoundingMissing addends
The Secret of Starfish Island
The legendary Golden Compass has vanished from the Explorer Cabin! The Island Guide needs your help. One of the visitors took it. Follow the clues to 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 | Navigation Gear | Survival Tool | Writing Hand | Cap Color | Fear |
|---|---|---|---|---|---|
| Jack | Spy Glass | Camp Lantern | Right Handed | Blue Cap | Afraid of Spiders |
| Ruby | Spy Glass | Camp Lantern | Right Handed | Blue Cap | Afraid of Caves |
| Grace | Spy Glass | Signal Whistle | Left Handed | Red Cap | Afraid of Spiders |
| Max | Sun Compass | Camp Lantern | Right Handed | Green Cap | Afraid of Heights |
| Zoe | Star Chart | Signal Whistle | Right Handed | Green Cap | Afraid of Spiders |
| Finn | Pocket Radar | Camp Lantern | Left Handed | Green Cap | Afraid of Caves |
| Emma | Bronze Map | Pocket Knife | Right Handed | Green Cap | Afraid of Spiders |
| Noah | Sun Compass | Pocket Knife | Left Handed | Green Cap | Afraid of Spiders |
| Lily | Sun Compass | Climbing Rope | Right Handed | Green Cap | Afraid of Spiders |
| Mia | Sun Compass | Camp Lantern | Left Handed | Blue Cap | Afraid of Heights |
| Ella | Spy Glass | Pocket Knife | Left Handed | Red Cap | Afraid of Spiders |
| Ben | Sun Compass | Signal Whistle | Right Handed | Blue Cap | Afraid of Caves |
| Cole | Bronze Map | Water Filter | Right Handed | Green Cap | Afraid of Spiders |
| Leo | Pocket Radar | Pocket Knife | Right Handed | Green Cap | Afraid of Caves |
| Ava | Sun Compass | Pocket Knife | Right Handed | Green Cap | Afraid of Spiders |
| Maya | Star Chart | Water Filter | Right Handed | Blue Cap | Afraid of Spiders |
| Annie | Bronze Map | Camp Lantern | Left Handed | Red Cap | Afraid of Heights |
| Toby | Pocket Radar | Climbing Rope | Left Handed | Blue Cap | Afraid of Heights |
| Owen | Star Chart | Signal Whistle | Left Handed | Green Cap | Afraid of Heights |
| Clara | Bronze Map | Water Filter | Right Handed | Blue Cap | Afraid of Heights |
| Jake | Star Chart | Camp Lantern | Right Handed | Green Cap | Afraid of Heights |
Clue 1
Place value
To unlock the secret diary of the island we must decode the page numbers using their place values. This reveals our first 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
3000
60
20
T
3000
60
400
20
40
7000
50
20
300
800
50
T
3000
9000
300
20
100
300
400
10
800
100
4000
5000
60
400
300
T
3000
4000
20
What is the value of the 3 in 23,570?T
What is the value of the 5 in 5,893?W
What is the value of the 6 in 7,065?H
What is the value of the 1 in 5,133?A
What is the value of the 4 in 948?F
What is the value of the 7 in 17,219?D
What is the value of the 1 in 7,317?G
What is the value of the 2 in 829?E
What is the value of the 5 in 950?O
What is the value of the 3 in 310?S
What is the value of the 9 in 49,206?U
What is the value of the 8 in 2,804?N
What is the value of the 4 in 64,378?L
What is the value of the 4 in 478?I
0/14 letters found
Clue 2
Addition
We count the total number of footprints found near the dock. Adding up all the tracks helps us narrow down who went where.
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
2334
6334
4052
T
2334
6334
6502
4052
7707
7888
9558
4052
2684
T
2334
6334
4052
6502
6086
6086
6502
6560
6334
T
2334
6334
9598
9177
2684
T
2334
6655
3827
6086
6502
T
2334
4052
1155 + 1179 =T
1531 + 1153 =D
4074 + 2012 =R
3324 + 5853 =N
4570 + 1990 =G
1649 + 2178 =W
3000 + 3502 =I
4084 + 5514 =A
4128 + 3760 =U
2910 + 3745 =O
1284 + 2768 =E
4786 + 2921 =F
4488 + 5070 =S
4319 + 2015 =H
0/14 letters found
Clue 3
Subtraction
The thief took some supplies from the camp. By subtracting the remaining gear from our list we find a clue left in the dirt.
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
5396
4492
5373
T
5396
4492
8006
5373
1732
5814
6846
2634
6846
4531
6846
1370
1732
5814
2303
1190
6846
3740
2303
8410
4531
5373
8410
7438 - 2042 =T
2282 - 912 =Y
6507 - 1134 =E
10828 - 2418 =B
9485 - 4954 =W
6676 - 4373 =O
8846 - 4354 =H
3452 - 2262 =M
7868 - 2054 =R
9536 - 1530 =I
8247 - 1401 =A
3976 - 2244 =F
8218 - 4478 =C
5119 - 2485 =N
0/14 letters found
Clue 4
Rounding
Our island radar only displays rounded distances to the nearest ten miles. We use this rounded data to track the suspect.
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
70
90
200
2000
7000
430
90
2900
200
500
300
3000
290
2900
370
370
2000
1300
900
300
90
5000
170
A
70
430
3000
300
50
2000
4300
Round 73 to the nearest tenA
Round 2,168 to the nearest thousandN
Round 908 to the nearest hundredL
Round 46 to the nearest tenU
Round 6,503 to the nearest thousandY
Round 2,663 to the nearest thousandF
Round 429 to the nearest tenS
Round 4,502 to the nearest thousandH
Round 191 to the nearest hundredI
Round 90 to the nearest tenT
Round 2,913 to the nearest hundredR
Round 289 to the nearest tenG
Round 369 to the nearest tenE
Round 484 to the nearest hundredP
Round 347 to the nearest hundredO
Round 173 to the nearest tenW
Round 1,256 to the nearest hundredC
Round 4,266 to the nearest hundredD
0/18 letters found
Clue 5
Missing addends — the last clue
We must balance the weight on the rope bridge. Finding the missing weight lets us safely cross and find 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
8 + ___ = 20
14 + ___ = 22
40 + ___ = 42
9 + ___ = 16
18 + ___ = 28
30 + ___ = 36
38 + ___ = 41
40 + ___ = 51
21 + ___ = 22
27 + ___ = 32
38 + ___ = 42
Step 2 — cross out the sentence with each answer
1.The villain creeps past the sleeping parrots, then ducks under the giant ferns.
2.The villain sneaks through the thick jungle, then ducks under the giant ferns.
3.The villain crosses the shaky rope bridge, then escapes into the hidden cave.
4.The villain sneaks through the thick jungle, then runs down the sandy beach.
5.The villain paddles across the quiet lagoon, then ducks under the giant ferns.
6.The villain climbs up the ancient stone steps, then ducks under the giant ferns.
7.The villain creeps past the sleeping parrots, then slips into the old shipwreck.
8.The villain climbs up the ancient stone steps, then hides behind the banana trees.
9.The villain climbs up the ancient stone steps, then escapes into the hidden cave.
10.The villain creeps past the sleeping parrots, then escapes into the hidden cave.
11.The villain creeps past the sleeping parrots, then hides behind the banana trees.
12.The villain sneaks through the thick jungle, then hides behind the banana trees.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Secret of Starfish Island
Culprit: Lily (Sun Compass · Climbing Rope · Right Handed · Green Cap · Afraid of Spiders)
- Clue 1 (Place value): "THE THIEF DOES NOT USE A SIGNAL WHISTLE"What is the value of the 3 in 23,570? = 3000 (T) · What is the value of the 5 in 5,893? = 5000 (W) · What is the value of the 6 in 7,065? = 60 (H) · What is the value of the 1 in 5,133? = 100 (A) · What is the value of the 4 in 948? = 40 (F) · What is the value of the 7 in 17,219? = 7000 (D) · What is the value of the 1 in 7,317? = 10 (G) · What is the value of the 2 in 829? = 20 (E) · What is the value of the 5 in 950? = 50 (O) · What is the value of the 3 in 310? = 300 (S) · What is the value of the 9 in 49,206? = 9000 (U) · What is the value of the 8 in 2,804? = 800 (N) · What is the value of the 4 in 64,378? = 4000 (L) · What is the value of the 4 in 478? = 400 (I)
- Clue 2 (Addition): "THE THIEF USED THEIR RIGHT HAND TO WRITE"1155 + 1179 = 2334 (T) · 1531 + 1153 = 2684 (D) · 4074 + 2012 = 6086 (R) · 3324 + 5853 = 9177 (N) · 4570 + 1990 = 6560 (G) · 1649 + 2178 = 3827 (W) · 3000 + 3502 = 6502 (I) · 4084 + 5514 = 9598 (A) · 4128 + 3760 = 7888 (U) · 2910 + 3745 = 6655 (O) · 1284 + 2768 = 4052 (E) · 4786 + 2921 = 7707 (F) · 4488 + 5070 = 9558 (S) · 4319 + 2015 = 6334 (H)
- Clue 3 (Subtraction): "THE THIEF RAN AWAY FROM A COBWEB"7438 - 2042 = 5396 (T) · 2282 - 912 = 1370 (Y) · 6507 - 1134 = 5373 (E) · 10828 - 2418 = 8410 (B) · 9485 - 4954 = 4531 (W) · 6676 - 4373 = 2303 (O) · 8846 - 4354 = 4492 (H) · 3452 - 2262 = 1190 (M) · 7868 - 2054 = 5814 (R) · 9536 - 1530 = 8006 (I) · 8247 - 1401 = 6846 (A) · 3976 - 2244 = 1732 (F) · 8218 - 4478 = 3740 (C) · 5119 - 2485 = 2634 (N)
- Clue 4 (Rounding): "A TINY STRIP OF GREEN CLOTH WAS FOUND"Round 73 to the nearest ten = 70 (A) · Round 2,168 to the nearest thousand = 2000 (N) · Round 908 to the nearest hundred = 900 (L) · Round 46 to the nearest ten = 50 (U) · Round 6,503 to the nearest thousand = 7000 (Y) · Round 2,663 to the nearest thousand = 3000 (F) · Round 429 to the nearest ten = 430 (S) · Round 4,502 to the nearest thousand = 5000 (H) · Round 191 to the nearest hundred = 200 (I) · Round 90 to the nearest ten = 90 (T) · Round 2,913 to the nearest hundred = 2900 (R) · Round 289 to the nearest ten = 290 (G) · Round 369 to the nearest ten = 370 (E) · Round 484 to the nearest hundred = 500 (P) · Round 347 to the nearest hundred = 300 (O) · Round 173 to the nearest ten = 170 (W) · Round 1,256 to the nearest hundred = 1300 (C) · Round 4,266 to the nearest hundred = 4300 (D)
- Clue 5 (Missing addends): surviving statement (box 9) → Lily8 + ___ = 20 = 12 · 14 + ___ = 22 = 8 · 40 + ___ = 42 = 2 · 9 + ___ = 16 = 7 · 18 + ___ = 28 = 10 · 30 + ___ = 36 = 6 · 38 + ___ = 41 = 3 · 40 + ___ = 51 = 11 · 21 + ___ = 22 = 1 · 27 + ___ = 32 = 5 · 38 + ___ = 42 = 4
About this mystery
- Grade level
- Grade 4 math
- Math topics
- Place value, Addition, Subtraction, Rounding, Missing addends
- Reading level
- grades 3-4
- Theme
- The Secret of Starfish Island — set in Starfish Island
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects