Knowing Our Numbers
Problems for Practice
Q 1). Estimate each of the following using a general rule.
a). 730 + 998 b). 796 – 314
c). 12,901 + 2,888 d). 28.292 – 21,496
Make ten more examples of addition, subtraction and estimation of their outcome.
a). 730 + 998
Estimation: 700 + 1000
= 1700
b). 796 – 314
Estimation: 800 – 300
= 500
c). 12,901 + 2,888
Estimation: 13000 + 3000
= 16000
d). 28.292 – 21,496
Estimation: 28000 – 21000
= 7000
Make ten more examples of addition, subtraction and estimation of their outcome.
Addition:
a). 520 + 780
= 500 + 800
= 1300
b). 796 + 314
Estimation: 800 + 300
= 1100
c). 10,901 + 4,998
Estimation: 11000 + 5000
= 16000
d). 18,992 + 20,096
Estimation: 19000 + 20000
= 39000
e). 2848 + 8954
Estimation: 3000 + 9000
= 12000
Subtraction:
a). 720 – 380
= 700 – 400
= 300
b). 796 – 314
Estimation: 800 – 300
= 500
c). 10,901 – 4,998
Estimation: 11000 – 5000
= 6000
d). 28,992 – 20,096
Estimation: 29000 – 20000
= 9000
e). 9848 – 8954
Estimation: 10000 – 9000
= 1000
Q 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 + 4,317 b). 1,08,734 – 47,599
c). 8325- 491 d). 4,89,348 – 48.365
Make four more such examples.
a). 439 + 334 + 4,317
rounding off to nearest hundreds: 400 + 300 + 4300
= 5000
rounding off to nearest tens: 440 + 330 + 4320
= 5090
b). 1,08,734 – 47,599
rounding off to nearest hundreds: 108700 – 47600
= 61100
rounding off to nearest tens: 108730 – 47600
= 61130
c). 8325- 491
rounding off to nearest hundreds: 8300 – 500
= 7800
rounding off to nearest tens: 8330 – 490
= 7840
d). 4,89,348 – 48,365
rounding off to nearest hundreds: 489300 – 48400
= 440900
rounding off to nearest tens: 489350 – 48370
= 980
Q 3). Estimate the following products using the general rule:
a). 578 X 161 b). 5281 X 3491
c). 1291 X 592 d). 9250 X 29
Make four more such examples.
Answers:
a). 578 X 161
Estimation: 600 X 200
= 1,20,000
b). 5281 X 3491
Estimation: 5000 X 3000
= 1,50,00,000
c). 1291 X 592
Estimation: 1300 X 600
= 7,80,000
d). 9250 X 29
Estimation: 9000 X 30
= 2,70,000
Make four more such examples.
a). 428 X 1250 b). 4687 X 3214
c). 4387 X 395 d). 8240 X 191
Answers:
a). 428 X 1250
Estimation: 400 X 1000
= 4,00,000
b). 4687 X 3214
Estimation: 5000 X 3000
= 1,50,00,000
c). 4387 X 395
Estimation: 4000 X 400
= 16,00,000
d). 6240 X 191
Estimation: 6000 X 200
= 12,00,000
Page 19
Try These
Round these numbers to the nearest tens.
28 32 52 41 39 48 64
59 99 215 1453 2936
Answer:
| Number | 28 | 32 | 52 | 41 | 39 | 48 | 64 | 59 | 99 | 215 | 1453 | 2936 |
| Nearest tens | 30 | 30 | 50 | 40 | 40 | 50 | 60 | 60 | 100 | 220 | 1450 | 2940 |
Rounding off to nearest Hundreds
Check if the following rounding off is correct or not:
841 – 800 9537 – 9500 49730- 49700
2546 – 2500 286- 200 5750 – 5800
168- 200 149- 100 9870- 9800
Correct those which are wrong.
Answer:
841 – 800 correct
9537- 9500 correct
49730- 49700 correct
2546- 2500 correct
286- 200 Wrong Correct answer is 300
5750 – 5800 correct
168 – 200 correct
149 – 100 correct
9870 – 9800 wrong correct answer is 9900.
Rounding off to nearest Thousands
Check if the following rounding off is correct or not:
2573 – 3000 53552 – 53000 6404 – 6000
65437 – 65000 7805 – 7000 3499 – 4000
Correct those which are wrong.
Answer:
2573 – 3000 correct
53552 – 53000 wrong correct answer is 54000
6404 – 6000 correct
65437 – 65000 correct
7805 – 7000 wrong correct answer is 8000
3499 – 4000 wrong correct answer is 3000.
Page 20
Rounding off the given numbers to the nearest tens, hundreds and thousands.
| Number | Nearest tens | Nearest hundreds | Nearest thousands | Nearest ten thousands |
| 75847 | 75850 | 75800 | 7600 | 80000 |
Page 22
Estimate the following products:
a). 87 X 313
b). 9 X 795
c). 898 X 785
d) 958 X 387
Answer:
a). 87 X 313
87 X 313 = 90 X 300
= 27000
b). 9 X 795
9 X 795 = 10 X 800
= 8000
c). 898 X 785
898 X 785 = 900 X 800
= 720000
d) 958 X 387
958 X 387 = 1000 X 400
= 400000
Knowing Our Numbers
