Chapter 1
EXERCISE 1.3
Question 1. Estimate each of the following using general rule:
(a) 730 + 998
(b) 796 – 314
(c) 12904 + 2888
(d) 28292 – 21496
Make ten more such examples of addition, subtraction and estimation of their outcome.
Answer:-
(a) 730 + 998
Round off to hundreds
730 is rounds off to 700
998 is rounds off to 1000
Hence, 730 + 998 = 700 + 1000 = 1700
(b) 796 – 314
Round off to hundreds
796 is rounds off to 800
314 is rounds off to 300
Hence, 796 – 314 = 800 – 300 = 500
(c) 12904 + 2888
Round off to thousands
12904 is rounds off to 13000
2888 is rounds off to 3000
Hence, 12904 + 2888 = 13000 + 3000 = 16000
(d) 28292 – 21496
Round off to thousands
28292 is round off to 28000
21496 is round off to 21000
Hence, 28292 – 21496 = 28000 – 21000 = 7000
SOLVE IT :-Ten more such examples are
(i) 420 + 380
= 400 + 400 = ?
(ii) 3837 + 4980
= 4000 + 5000 = ?
(iii) 5387 – 2772
= 5000 – 3000 = ?
(iv) 3820 – 2360
= 4000 – 2000 = ?
(v) 1375 + 1806
= 1000 + 2000 = ?
(vi) 1985 – 1750
= 2000 – 2000 = ?
(vii) 1910 + 4975
= 2000 + 5000 = ?
(viii) 6382 + 6800
= 6000 + 7000 =?
(ix) 2952 -860
= 2000 - 900=?
(x) 536 – 437
= 500 – 400 = ?
Question 2. 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) 1,08,734 – 47,599
(c) 8325 – 491
(d) 4,89,348 – 48,365
Make four more such examples.
Answer:-
(a) 439 + 334 + 4317
Rounding off to nearest hundreds
439 + 334 + 4317 = 400 + 300 + 4300=5000
Rounding off to nearest tens
439 + 334 + 4317 = 440 + 330 + 4320 =5090
(b) 1,08,734 – 47,599
Rounding off to nearest hundreds
1,08,734 – 47,599 = 1,08,700 – 47,600=61,100
Rounding off to nearest tens
1,08,734 – 47,599 = 1,08,730 – 47,600=61,130
(c) 8325 – 491
Rounding off to nearest hundreds
8325 – 491 = 8300 – 500=7800
Rounding off to nearest tens
8325 – 491 = 8330 – 490=7840
(d) 4,89,348 – 48,365
Rounding off to nearest hundreds
4,89,348 – 48,365 = 4,89,300 – 48,400 =4,40,900
Rounding off to nearest tens
4,89,348 – 48,365 = 4,89,350 – 48,370=4,40,980
Four more examples are as follows
(i) 5725+654
(ii) 8927-7820
(iii) 5732+7865
(iv) 7852-5826
Question 3. Estimate the following products using general rule:
(a) 578 * 161
(b) 5281 * 3491
(c) 1291 * 592
(d) 9250 * 29
Make four more such examples.
Answer:-
(a) 578 * 161
Rounding off by general rule
598 and 161 rounded off to 600 and 200 respectively
600 *200=1,20,000
(b) 5281*3491
Rounding off by general rule
5281 and 3491 rounded off to 5000 and 3500 respectively
5000*3500=17,500,000
(c) 1291 * 592
Rounding off by general rule
1291 and 592 rounded off to 1300 and 600 respectively
1300*600=7,800,000
(d) 9250 * 29
Rounding off by general rule
9250 and 29 rounded off to 9000 and 30 respectively
9000*30=2,70,000
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