EXERCISE 1.3
1) Estimate:
1.a) 730 + 998
Ans. Rounding off to hundreds
730 = 700
998 = 1000
Hence 730 + 998 = 700 + 100
= 1700
1.b) 796 – 314
Ans. Rounding off to hundreds
796 = 800
314 = 300
Hence 796 – 314 = 800 – 300
= 500
1.c) 12,904 + 2,888
Ans. Rounding off to thousands
12,904 = 13,000
2,888 = 3,000
Hence 12,904 + 2,888 = 13,000 + 3000
= 16000
1.d) 28,292 – 21,496
Ans. Rounding off to thousands
28,292 = 28,000
21,496 = 21,000
Hence 28,292 – 21,496 = 28,000 – 21,000
= 7,000
Make ten more such examples of addition, subtraction and estimation of their outcome.
a). 422 + 319
Ans.
422 = 400
319 = 300
400 – 300 = 100
b). 5,432 – 1,692
Ans.
5,432 = 5,000
1,692 = 2,000
5,000 – 2,000 = 3000
c). 7,214 – 3,807
Ans.
7,214 = 7,000
3,807 = 4,000
7,000 – 4,000 = 3,000
d). 569 – 319
Ans.
569 = 600
319 = 300
600 – 300 = 300
e). 639 + 587
Ans.
639 = 600
587 = 600
600 + 600 = 1200
f). 1697 – 876
Ans.
1,697 = 2,000
876 = 900
2,000 – 900 = 1,100
g). 6,772 + 5329
Ans.
6,772 = 7,000
5,329 = 5,000
7,000 + 5,000 = 12,000
h). 3,692 + 2269
Ans.
3,692 = 4,000
2,269 = 2,000
4,000 + 2,000 = 6,000
i). 8,762 – 4,921
Ans.
8,762 = 9,000
4,921 = 5,000
9,000 – 5,000 = 4,000
j). 2,659 + 4,217
Ans.
2,659 = 3,000
4,217 = 4,000
3,000 + 4,000 = 7,000
2) Give a rough estimate (by rounding off to nearest hundred) and also a closer estimate
(by rounding off to nearest tens):
a) 439 + 334 + 4,317
Ans. Rounding off to nearest hundreds
439 + 334 + 4,317 = 400 + 300 + 4,300
= 5,000
Rounding off to nearest tens
439 + 334 + 4,317 = 440 + 330 + 4,320
= 5,090
b) 1,08,734 – 47,599
Ans. Rounding off to nearest hundred
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) 8,325 – 491
Ans. Rounding off to nearest hundreds
8,325 – 491 = 8,300 – 500
= 7,800
Rounding off to nearest tens
8,325 – 491 = 8,330 – 490
= 7,840
d) 4,89,348 – 48,365
Ans. 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 = 4,89,300 – 48,400
= 4,40,900
Make four more of such examples
a) 5,621 – 1,219
Ans Rounding off to nearest hundred
5,621 – 1,219 = 5,600 – 1,220
=4,400
Rounding off to nearest tens
5,621 – 1,219 = 5,620 – 1,220
= 4,400
b) 337 + 769 + 438
Ans. Rounding off to nearest hundred
337 + 769 + 438 = 300 + 800 + 400
= 1,500
Rounding off to nearest tens
337 + 769 + 438 = 340 + 770 + 440
= 1,550
c) 12,762 + 3,593
Ans. Rounding off to nearest hundred
12,762 + 3,593 = 12,800 + 3,600
= 16,400
Rounding off to nearest tens
12,762 + 3,593 = 12,760 + 3,590
= 16,350
d) 9,737 – 3,871
Ans Rounding off to nearest hundred
9,737 – 3,871 = 9,700 – 3,900
= 5,800
Rounding off to nearest tens
9,737 – 3,871 = 9,740 – 3,870
= 5,870