🔎 Math MysteriesGrade 4Reading: grades 3-4AdditionMultiplicationSkip countingRoundingDivision
The Case of the Golden Calculator
The Golden Calculator has vanished from the Infinity Academy vault! The Mathletes must decode the clues and find the culprit.
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 tool | special gear | erasing hand | headwear | cleared obstacle |
|---|---|---|---|---|---|
| Dorothy Vaughan | grid net | number boots | right eraser | green visor | fraction block |
| Pythagoras | fraction wand | number boots | right eraser | blue helmet | fraction block |
| Rene Descartes | grid net | number boots | left eraser | symbol cap | prime door |
| Benoit Mandelbrot | laser protractor | number boots | right eraser | blue helmet | fraction block |
| Euclid | fraction wand | binary belt | right eraser | blue helmet | prime door |
| Grace Hopper | equation blaster | matrix cape | right eraser | blue helmet | prime door |
| Mary Jackson | laser protractor | number boots | left eraser | blue helmet | fraction block |
| Aryabhata | laser protractor | led visor | right eraser | blue helmet | prime door |
| Ada Lovelace | laser protractor | matrix cape | left eraser | blue helmet | fraction block |
| Carl Gauss | infinite ruler | digit gloves | right eraser | blue helmet | fraction block |
| Benjamin Banneker | laser protractor | led visor | right eraser | blue helmet | fraction block |
| Charles Babbage | fraction wand | binary belt | right eraser | green visor | fraction block |
| John Venn | laser protractor | led visor | left eraser | symbol cap | prime door |
| Isaac Newton | fraction wand | led visor | left eraser | symbol cap | sudoku maze |
| Leonhard Euler | laser protractor | digit gloves | left eraser | green visor | fraction block |
| Ada Byron | infinite ruler | matrix cape | right eraser | blue helmet | fraction block |
| Emmy Noether | laser protractor | led visor | right eraser | symbol cap | fraction block |
| Blaise Pascal | equation blaster | digit gloves | right eraser | green visor | prime door |
| Albert Einstein | equation blaster | digit gloves | left eraser | symbol cap | sudoku maze |
| Katherine Johnson | equation blaster | led visor | left eraser | blue helmet | fraction block |
| Alan Turing | equation blaster | digit gloves | right eraser | symbol cap | sudoku maze |
Clue 1
Addition
We count up the chalk supply boxes left in the hallway. Adding the boxes together gives us the code for 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
9637
2315
3823
T
9637
2315
7633
3823
9052
2068
8755
3823
8429
7004
8755
T
9637
9092
3823
7157
2920
T
9637
2315
3823
5234
3823
2068
2639
7633
8429
8755
2920
5588 + 4049 =T
4189 + 2968 =A
6029 + 3063 =W
632 + 1436 =D
2745 + 6307 =F
983 + 1937 =R
3840 + 4915 =O
2724 + 2510 =L
5654 + 2775 =S
4167 + 2837 =N
1253 + 2570 =E
818 + 1821 =V
717 + 1598 =H
3832 + 3801 =I
0/14 letters found
Clue 2
Multiplication facts (1-12)
The lockers are arranged in neat rows and columns. Multiplying the rows by the columns points us to the next secret note.
Solve each problem to learn its letter. Then write that letter in every box that shows the same number, and read the secret clue.
R
55
36
88
9
80
9
81
56
5
10
5
10
R
55
81
45
10
R
55
110
81
R
55
108
45
144
10
R
55
10
90
21
54
56
5
5 × 11 =R
6 × 9 =U
9 × 9 =A
7 × 3 =O
10 × 9 =F
10 × 11 =M
11 × 8 =G
8 × 7 =N
8 × 10 =T
1 × 9 =H
12 × 12 =W
12 × 3 =I
9 × 12 =K
9 × 5 =S
2 × 5 =E
1 × 5 =D
0/16 letters found
Clue 3
Skip counting
We follow a trail of numbered floor tiles. Skip counting by fives helps us skip the traps and reach the third 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
90
21
55
22
33
60
16
130
55
100
T
90
42
27
42
130
26
55
T
90
21
55
33
35
60
28
T
90
16
42
18
40
130
42
28
65
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110T
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120D
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, ___, 30, 33S
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30V
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39F
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26Y
Skip-count by 10s. Fill the blank: 10, 20, 30, ___, 50, 60B
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, ___, 40, 45R
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75K
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, ___, 24, 27H
Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65E
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, ___, 21, 24N
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, ___, 18, 20I
Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48O
Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32C
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150L
Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, ___, 70, 80A
0/17 letters found
Clue 4
Rounding
A digital scale flashes a blurry weight reading. Rounding the number to the nearest ten reveals the locker combination.
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
500
2900
900
170
A
500
9000
900
3700
2000
170
3000
1100
A
500
1700
370
700
110
3700
110
370
1100
110
9000
4300
A
500
2900
2000
3000
700
130
1300
Round 501 to the nearest hundredA
Round 1,660 to the nearest hundredB
Round 173 to the nearest tenR
Round 127 to the nearest tenN
Round 367 to the nearest tenL
Round 1,291 to the nearest hundredD
Round 2,111 to the nearest thousandF
Round 2,936 to the nearest hundredS
Round 4,297 to the nearest hundredW
Round 3,076 to the nearest thousandO
Round 1,091 to the nearest hundredM
Round 3,745 to the nearest hundredH
Round 901 to the nearest hundredC
Round 9,172 to the nearest thousandT
Round 112 to the nearest tenE
Round 679 to the nearest hundredU
0/16 letters found
Clue 5
Division facts (1-12) — the last clue
We find a deck of logic cards that must be shared equally. Dividing the cards among the team gives each of us a final clue piece.
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
2 ÷ 2 = ?
16 ÷ 2 = ?
14 ÷ 7 = ?
11 ÷ 1 = ?
84 ÷ 7 = ?
28 ÷ 4 = ?
4 ÷ 1 = ?
60 ÷ 10 = ?
45 ÷ 9 = ?
9 ÷ 1 = ?
24 ÷ 8 = ?
Step 2 — cross out the sentence with each answer
1.The villain measured with the infinite ruler, then wrapped up in the matrix cape.
2.The villain measured with the infinite ruler, then activated the digit gloves.
3.The villain fired the equation blaster, then turned on the led visor.
4.The villain swung the laser protractor, then turned on the led visor.
5.The villain measured with the infinite ruler, then jumped high in number boots.
6.The villain waved the fraction wand, then turned on the led visor.
7.The villain fired the equation blaster, then wrapped up in the matrix cape.
8.The villain waved the fraction wand, then jumped high in number boots.
9.The villain measured with the infinite ruler, then turned on the led visor.
10.The villain swung the laser protractor, then jumped high in number boots.
11.The villain fired the equation blaster, then activated the digit gloves.
12.The villain threw the grid net, then turned on the led visor.
Solve it
Name the culprit
Choose the one suspect left standing.
Answer Key — The Case of the Golden Calculator
Culprit: Benoit Mandelbrot (laser protractor · number boots · right eraser · blue helmet · fraction block)
- Clue 1 (Addition): "THE THIEF DOES NOT WEAR THE LED VISOR"5588 + 4049 = 9637 (T) · 4189 + 2968 = 7157 (A) · 6029 + 3063 = 9092 (W) · 632 + 1436 = 2068 (D) · 2745 + 6307 = 9052 (F) · 983 + 1937 = 2920 (R) · 3840 + 4915 = 8755 (O) · 2724 + 2510 = 5234 (L) · 5654 + 2775 = 8429 (S) · 4167 + 2837 = 7004 (N) · 1253 + 2570 = 3823 (E) · 818 + 1821 = 2639 (V) · 717 + 1598 = 2315 (H) · 3832 + 3801 = 7633 (I)
- Clue 2 (Multiplication facts (1-12)): "RIGHT HANDED ERASER MARKS WERE FOUND"5 × 11 = 55 (R) · 6 × 9 = 54 (U) · 9 × 9 = 81 (A) · 7 × 3 = 21 (O) · 10 × 9 = 90 (F) · 10 × 11 = 110 (M) · 11 × 8 = 88 (G) · 8 × 7 = 56 (N) · 8 × 10 = 80 (T) · 1 × 9 = 9 (H) · 12 × 12 = 144 (W) · 12 × 3 = 36 (I) · 9 × 12 = 108 (K) · 9 × 5 = 45 (S) · 2 × 5 = 10 (E) · 1 × 5 = 5 (D)
- Clue 3 (Skip counting): "THEY FAILED TO SOLVE THE FRACTION BLOCK"Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, ___, 100, 110 = 90 (T) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, ___, 110, 120 = 100 (D) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, ___, 30, 33 = 27 (S) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, ___, 28, 30 = 26 (V) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ___, 36, 39 = 33 (F) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ___, 24, 26 = 22 (Y) · Skip-count by 10s. Fill the blank: 10, 20, 30, ___, 50, 60 = 40 (B) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, ___, 40, 45 = 35 (R) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, ___, 70, 75 = 65 (K) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, ___, 24, 27 = 21 (H) · Skip-count by 5s. Fill the blank: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, ___, 60, 65 = 55 (E) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, ___, 21, 24 = 18 (N) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, ___, 18, 20 = 16 (I) · Skip-count by 3s. Fill the blank: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, ___, 45, 48 = 42 (O) · Skip-count by 2s. Fill the blank: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, ___, 30, 32 = 28 (C) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, ___, 140, 150 = 130 (L) · Skip-count by 10s. Fill the blank: 10, 20, 30, 40, 50, ___, 70, 80 = 60 (A)
- Clue 4 (Rounding): "A SCRATCH FROM A BLUE HELMET WAS FOUND"Round 501 to the nearest hundred = 500 (A) · Round 1,660 to the nearest hundred = 1700 (B) · Round 173 to the nearest ten = 170 (R) · Round 127 to the nearest ten = 130 (N) · Round 367 to the nearest ten = 370 (L) · Round 1,291 to the nearest hundred = 1300 (D) · Round 2,111 to the nearest thousand = 2000 (F) · Round 2,936 to the nearest hundred = 2900 (S) · Round 4,297 to the nearest hundred = 4300 (W) · Round 3,076 to the nearest thousand = 3000 (O) · Round 1,091 to the nearest hundred = 1100 (M) · Round 3,745 to the nearest hundred = 3700 (H) · Round 901 to the nearest hundred = 900 (C) · Round 9,172 to the nearest thousand = 9000 (T) · Round 112 to the nearest ten = 110 (E) · Round 679 to the nearest hundred = 700 (U)
- Clue 5 (Division facts (1-12)): surviving statement (box 10) → Benoit Mandelbrot2 ÷ 2 = 1 · 16 ÷ 2 = 8 · 14 ÷ 7 = 2 · 11 ÷ 1 = 11 · 84 ÷ 7 = 12 · 28 ÷ 4 = 7 · 4 ÷ 1 = 4 · 60 ÷ 10 = 6 · 45 ÷ 9 = 5 · 9 ÷ 1 = 9 · 24 ÷ 8 = 3
About this mystery
- Grade level
- Grade 4 math
- Math topics
- Addition, Multiplication, Skip counting, Rounding, Division
- Reading level
- grades 3-4
- Theme
- The Case of the Golden Calculator — set in Infinity Academy
- Format
- Interactive online & printable worksheet with answer key
- Solution
- One unique, verified culprit among 21 suspects