Chapter 1: Knowing Your Numbers
Exercise 1.3
Q1. Estimate each of the following using general rule:
(a) 730 + 998
(b) 796 – 314
(c) 12,904 + 2,888
(d) 28,292 – 21,496
Answer.
(a) 730 round off to 700
998 round off to 1000
Estimated sum = 1700
(b) 796 round off to 800
314 round off to 300
Estimated difference = 500
(c) 12,904 round off to 13,000
2,888 round off to 3,000
Estimated sum = 16,000
(d) 28,292 round off to 28,000
21,496 round off to 21,000
Estimated difference= 7,000
Q2. Give a rough estimate (by rounding off to nearest hundreds) and also a closer estimate (by rounding off to nearest tens):
(a) 439 + 334 + 4317
(b) 1,08,737 – 47,599
(c) 8325 – 491
(d) 4,89,348 – 48,365
Answer.
(a) 439 round off to 400
334 round off to 300
4,317 round off to 4,300
Estimated sum = 5,000
(b) 1,08,734 round off to 1,08,700
47,599 round off to 47,600
Estimated difference = 61,100
(c) 8,325 round off to 8,300
491 round off to 500
Estimated difference = 7,800
(d) 4,89,348 round off to 4,89,300
48,365 round off to 48,400
Estimated difference = 4,40,900
Q3. Estimate the following products using general rule:
(a) 578 x 161
(b) 5281 x 3491
(c) 1291 x 592
(d) 9250 x 29
Answer.
(a) 578 x 161
578 round off to 600
161 round off to 200
The estimated product = 600 x 200 = 1,20,000
(b) 5281 x 3491
5,281 round of to 5,000
3,491 round off to 3,500
The estimated product = 5,000 x 3,500 = 1,75,00,000
(c) 1291 x 592
1,291 round off to 1,300
592 round off to 600
The estimated product = 1,300 x 600 = 7,80,000
(d) 9250 x 29
9,250 round off to 10,000
229 round off to 30
The estimated product = 10,000 x 30 = 3,00,000