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Problems on Numbers Questions and Answers

Important Instructions
61.

In a five digit number, the digit at the hundreds place is three-fourth of the digit at ten thousands place and the digit at tens place is two-third of the digit at hundreds place. The digit at tens place is square of the smallest prime number and the digit at thousands place is the largest single digit prime number. If the digit at unit place is the largest single digit odd number, then the number is

Exam Year(s)

CTET - 2021,

Answer: A

The number is 87649.

Fill in the digits from the clues, starting with the ones that are fixed directly:

\[ \begin{aligned} \text{tens} &= 2^{2} = 4 \\ \text{hundreds} &: \tfrac{2}{3} \times h = 4,\ h = 6 \\ \text{ten thousands} &: \tfrac{3}{4} \times t = 6,\ t = 8 \\ \text{thousands} &= 7,\quad \text{units} = 9 \end{aligned} \]

The smallest prime is 2, so the tens digit is 4. The largest single-digit prime is 7 and the largest single-digit odd number is 9. Reading from the ten thousands place: 8, 7, 6, 4, 9, giving 87649.

The other numbers fail at once: 49327 and 42937 have the wrong tens digit, and 83419 has 4 in the hundreds place, which is not three-fourths of 8.

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62.

The sum of five consecutive numbers is 20. What is the sum of first three consecutive numbers ?

Exam Year(s)

CTET - 2021,

Answer: B

The sum of the first three numbers is 9.

Five consecutive numbers have their middle number equal to their average:

\[ \begin{aligned} \text{middle} &= 20 \div 5 = 4 \\ \text{numbers} &= 2, 3, 4, 5, 6 \\ 2 + 3 + 4 &= 9 \end{aligned} \]

Check: 2 + 3 + 4 + 5 + 6 = 20. The answer 12 is 3 + 4 + 5, the middle three, and 5 is just 2 + 3, the first two.

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63.

A number becomes double if it is increased by 8. What is the number ?

Exam Year(s)

CTET - 2024,

Answer: B

The number is 8.

Let the number be \(x\). Increasing it by 8 doubles it:

\[ \begin{aligned} x + 8 &= 2x \\ x &= 8 \end{aligned} \]

Check: 8 + 8 = 16, which is double 8. For the other options, 6 + 8 = 14 (not 12), 12 + 8 = 20 (not 24) and 16 + 8 = 24 (not 32), so none of them doubles.

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64.

Sum of two numbers is 80. Greater number exceeds by 5 from four times of the smaller. Find the numbers?

Answer: A

Let the smaller be \( y \); the greater is \( 4y + 5 \).

\[ y + 4y + 5 = 80 \quad\Longrightarrow\quad 5y = 75 \]

\[ y = 15, \qquad \text{greater} = 65 \]

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65.

A number exceeds by 25 from its \(\dfrac{3}{8}\) part. Then the number is:

Answer: D

\[ x - \frac{3x}{8} = 25 \quad\Longrightarrow\quad \frac{5x}{8} = 25 \]

\[ x = 40 \]

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66.

If \(\dfrac{1}{3}\) of \(\dfrac{1}{4}\) of a number is 15, then \(\dfrac{3}{10}\) of that number is:

Answer: D

Let the number be \(x\)
Then, \(\dfrac{1}{3}\) of \(\dfrac{1}{4}\) of \(x = 15 \Leftrightarrow x =15 \times 12 = 180\)
So, required number
\(\left( \dfrac{3}{10} \times 180 \right) =54\)

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67.

A number consists of 3 digits whose sum is 10. The middle digit is equal to the sum of the other two and the number will be increased by 99 if its digits are reversed. The number is:

Answer: B

Let the middle digit be \(x.\)
Then, \(2x = 10\) or \(x = 5\). So, the number is either \(253 \text{ or } 352.\)
Since the number increases on reversing the digits, so the hundred's digits is smaller than the unit's digit.
Hence, required number \(= 253\)

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68.

The sum of the numbers is 264. If the first number be twice the second and third number be one-third of the first, then the second number is:

Answer: C

Let the second number be \(x\). Then, first number \(= 2x\) and third number \(= \dfrac{2x}{3}\)
\(2x + x + \dfrac{2x}{3} = 264\\ \Rightarrow \dfrac{11x}{3} = 264\\ \Rightarrow x = 72\)

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69.

A number consists of two digits. If the digits interchange places and the new number is added to the original number, then the resulting number will be divisible by:

Answer: D

Let the ten's digit be \(x\) and unit's digit be \(y\)
Then, number \(10x + y\)
Number obtained by interchanging the digits \(= 10y + x\)
\((10x + y) + (10y + x) = 11(x + y)\)
which is divisible by 11

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70.

The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 36. What is the difference between the two digits of that number?

Answer: B

Let the ten's digit be \(x\) and unit's digit be \(y\)
Then,
\((10x + y) - (10y + x) = 36\\ \Rightarrow 9(x - y) = 36\\ \Rightarrow x - y = 4\)

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