NCERT Exemplar Solutions
Class 6 - Mathematics - Unit 1: Number System - Multiple Choice Questions
Question 29

Question.  29

If \(7254*98\) is divisible by 22, the digit \(*)\) is

(A)

1

(B)

2

(C)

6

(D)

0

Detailed Answer with Explanation:

Key idea: A number divisible by 22 must be divisible by both 2 and 11.

Step 1: Check divisibility by 2
Last digit is 8, so it is divisible by 2.

Step 2: Check divisibility by 11
Use the alternating-sum rule: (sum of digits in odd places) − (sum of digits in even places) must be 0 or a multiple of 11.

Number: \(7\;2\;5\;4\;*\;9\;8\)

Odd places (1st, 3rd, 5th, 7th): \(7,\;5,\;*,\;8\)

Even places (2nd, 4th, 6th): \(2,\;4,\;9\)

Sum(odd) = \(7 + 5 + * + 8 = 20 + *\)

Sum(even) = \(2 + 4 + 9 = 15\)

Difference = \((20 + *) - 15 = * + 5\)

For divisibility by 11: \(* + 5\) must be \(0, 11, 22,\ldots\)

Since \(*)\) is a single digit (0–9), \(* + 5\) can be from 5 to 14.

The only value from \(\{5,6,\ldots,14\}\) that is a multiple of 11 is \(11\).

So, \(* + 5 = 11 \Rightarrow * = 6\).

Answer: \(6\) (Option C).

NCERT Exemplar Solutions Class 6 – Mathematics – Unit 1: Number System – Multiple Choice Questions | Detailed Answers