The total surface area of a cube is given below.
What is the volume of the cube?
One face = 1,350 ÷ 6 = 225 cm²
Edge = √225 = 15 cm
Volume = 15³ = 3,375 cm³
Trap: 225 is the area of one face.
Answer: 3,375 cm³
Square Roots & Cube Roots · Exercise 6 of 6
30 diagram-based Square Root and Cube Root questions in the style of current bank, SSC, railway and campus placement papers. Every question has its own figure to read: factor trees, square plots and cubes, ladder and diagonal triangles, number lines, unit-digit and long-division tables, Venn diagrams of squares and cubes, infinite-radical trees, number machines, given-value tables and area models.
The total surface area of a cube is given below.
What is the volume of the cube?
One face = 1,350 ÷ 6 = 225 cm²
Edge = √225 = 15 cm
Volume = 15³ = 3,375 cm³
Trap: 225 is the area of one face.
Answer: 3,375 cm³
A large cube is cut into small cubes of edge 2 cm, with nothing wasted.
How many small cubes are obtained?
Edge of large cube = ∛10,648 = 22 cm
Small cubes along each edge = 22 ÷ 2 = 11
Number = 11³ = 1,331
Trap: 5,324 divides the volume by 2, not by 2³.
Answer: 1,331
Four points are marked on the number line.
Which point is closest to √50?
7² = 49 and 8² = 64, so √50 is just above 7
√50 ≈ 7.07
That is point B
Trap: C sits halfway, but 50 is much closer to 49 than to 64.
Answer: B
P marks ∛40 and Q marks √40 on the number line.
How many whole numbers lie strictly between P and Q?
∛40: 3³ = 27 and 4³ = 64 → about 3.4
√40: 6² = 36 and 7² = 49 → about 6.3
Whole numbers between: 4, 5, 6 → 3
Trap: 2 forgets that 6 is below 6.3.
Answer: 3
The table gives the last digit of a square for each last digit of the number.
| Number ends in | 0 | 1 or 9 | 2 or 8 | 3 or 7 | 4 or 6 | 5 |
|---|---|---|---|---|---|---|
| Square ends in | 0 | 1 | 4 | 9 | 6 | 5 |
Which one of these numbers can be a perfect square?
Squares end only in 0, 1, 4, 5, 6 or 9
8,463 ends in 3, 9,127 in 7, 6,858 in 8 – all impossible
7,744 = 88² ✓
Trap: ending in 8 is ruled out by the table.
Answer: 7,744
The table pairs the last digit of a cube with the last digit of its cube root.
| Cube ends in | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|
| Root ends in | 1 | 8 | 7 | 4 | 5 | 6 | 3 | 2 | 9 |
571,787 is a perfect cube. What is its cube root?
Ends in 7 → root ends in 3
Front part 571: 8³ = 512 ≤ 571 < 729 = 9³ → tens digit 8
Cube root = 83
Trap: 87 keeps the 7 instead of using the table.
Answer: 83
A student found √7,056 by the long-division method. The last line is missing.
| Step | Working |
|---|---|
| Pair the digits | 70 | 56 |
| Largest square ≤ 70 | 8² = 64, remainder 6 |
| Bring down 56 | 656 |
| Double 8 → 16_; 16_ × _ ≤ 656 | 164 × 4 = 656, remainder 0 |
| Square root | ? |
What is √7,056?
First digit from 8² = 64 → 8
Next digit from 164 × 4 = 656 → 4
Remainder 0, so √7,056 = 84
Trap: 164 is the trial divisor, not the root.
Answer: 84
Study the pattern.
| Number | Square root |
|---|---|
| 1 | 1 |
| 121 | 11 |
| 12321 | 111 |
| 1234321 | 1111 |
| 123454321 | ? |
What is √123454321?
The number rises to 5 and falls back → five 1s in the root
√123454321 = 11111
Check: 11111² = 123454321 ✓
Trap: 12345 copies the rising digits.
Answer: 11111
The numbers 1 to 100 are sorted into perfect squares and perfect cubes.
How many numbers from 1 to 100 are neither perfect squares nor perfect cubes?
Squares or cubes = 8 + 2 + 2 = 12
(1 and 64 are both)
Neither = 100 − 12 = 88
Trap: 86 counts 1 and 64 twice.
Answer: 88
From 1 to 1000 there are 31 perfect squares and 10 perfect cubes.
How many numbers from 1 to 1000 are perfect squares but not perfect cubes?
Both = sixth powers: 1, 64, 729 → 3
Squares only = 31 − 3 = 28
Trap: 38 is squares or cubes (31 + 10 − 3).
Answer: 28
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