NCERT Exemplar Solutions
Class 6 - Mathematics - Unit 1: Number System - Problems and Solutions

Question 177

Idea: Round each number to the nearest hundred before adding.

Rounding rule (to nearest hundred)

• Look at the tens digit.
• If tens digit \(\ge 5\), round up to the next hundred.
• If tens digit \(\le 4\), round down to the previous hundred.

(a) 874 + 478

1. \(874:\) tens digit \(=7\) \(\Rightarrow\) round up \(\to 900\).
2. \(478:\) tens digit \(=7\) \(\Rightarrow\) round up \(\to 500\).
3. Estimated sum: \(900 + 500 = 1400\).

(b) 793 + 397

1. \(793:\) tens digit \(=9\) \(\Rightarrow\) round up \(\to 800\).
2. \(397:\) tens digit \(=9\) \(\Rightarrow\) round up \(\to 400\).
3. Estimated sum: \(800 + 400 = 1200\).

(c) 11244 + 3507

1. \(11244:\) tens digit \(=4\) \(\Rightarrow\) round down \(\to 11200\).
2. \(3507:\) tens digit \(=0\) \(\Rightarrow\) round down \(\to 3500\).
3. Estimated sum: \(11200 + 3500 = 14700\).

(d) 17677 + 13589

1. \(17677:\) tens digit \(=7\) \(\Rightarrow\) round up \(\to 17700\).
2. \(13589:\) tens digit \(=8\) \(\Rightarrow\) round up \(\to 13600\).
3. Estimated sum: \(17700 + 13600 = 31300\).