NCERT Solutions for Class 4th Maths Chapter 10 Adding a 2-digit number to its reverse — Reverse and Add

Book page 151 Updated on2026-09-19

Q1.

Take a 2-digit number say, 27. Reverse its digits (72). Add them (99). Repeat for different 2-digit numbers.

Answer

Take a number, turn the digits round, and add.

Why it happens: Each digit gets counted once as a ten and once as a one. So the sum is always the two digits added, taken 11 times.

Q2.

What sums can we get when we add a 2-digit number with its reverse?

Answer

We always get a number from the 11 table.

27 + 72 = 99 = 11 × 9    (2 + 7 = 9)
13 + 31 = 44 = 11 × 4    (1 + 3 = 4)
62 + 26 = 88 = 11 × 8    (6 + 2 = 8)

So the sums are 11, 22, 33, 44, 55, 66, 77, 88, 99, 110, … up to 198.

Why it happens: Add the two digits first. Whatever you get, the answer is that many elevens.

Try This: Guess before you add. For 46, the digits make 4 + 6 = 10, so the sum should be 110. Check: 46 + 64 = 110.

Q3.

List down all numbers which when added to their reverse give i) 55 ii) 88

Answer

First find how many elevens the sum is.

55 = 11 × 5 → the two digits must add to 5
88 = 11 × 8 → the two digits must add to 8

i) Sum 55

14, 23, 32, 41, 50

Check: 14 + 41 = 55, 23 + 32 = 55, 50 + 5 = 55.

ii) Sum 88

17, 26, 35, 44, 53, 62, 71, 80

Check: 17 + 71 = 88, 44 + 44 = 88, 80 + 8 = 88.

Why it happens: The sum only depends on the two digits added together, so every pair of digits that makes 5 works for 55.

Q4.

Can we get a 3-digit sum? What is the smallest 3-digit sum that we can get?

Answer

Yes, we can. The smallest 3-digit sum is 110.

Digits add to 9 → 11 × 9 = 99 (still 2 digits)
Digits add to 10 → 11 × 10 = 110 (3 digits)
Example: 19 + 91 = 110

Other numbers that give 110 are 28, 37, 46, 55, 64, 73, 82 and 91.

Why it happens: 99 is the biggest 2-digit answer. The very next answer in the 11 table is 110, so that is the smallest 3-digit sum.

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