Chapter 1 Knowing our Numbers Exercise 1.3
Question 1: Estimate each of the following using general rule:a) 730 + 998
b) 796 - 314
c) 12,904 + 2,888
d) 28,292 - 21,496
Make ten more such examples of addition, subtraction and estimation of their outcome.
Answer:
a)
Round off to hundreds
730 rounds off to 700
998 rounds off to 1000
= 700 + 1000 = 1700
b)
Round off to hundreds
796 rounds off to 800
314 rounds off to 300
= 800 - 300 = 500
c)
Round off to thousands
12904 rounds off to 13000
2888 rounds off to 3000
= 13000 + 3000 = 16000
d)
Round off to thousands
28292 round off to 28000
21496 round off to 21000
= 28000 - 21000 = 7000
Ten examples of such addition and subtraction are
i) 460 + 290
Round off to hundreds
460 round off to 500
290 round off to 300
= 500 + 300 = 800
ii) 3999 + 5100
Round off to thousands
3999 round off to 4000
5100 round off to 5000
= 4000 + 5000 = 9000
iii) 611 - 455
Round off to hundreds
611 round off to 600
455 round off to 500
= 600 - 500 = 100
iv) 5440 - 2972
Round off to thousands
5440 round off to 5000
2972 round off to 3000
= 5000 - 3000 = 2000
v) 2091 + 9845
Round off to thousands
2091 round off to 2000
9845 round off to 10000
= 2000 + 10000 = 12000
vi) 1990 - 1292
Round off to thousands
1990 round off to 2000
1292 round off to 1300
= 2000 - 1300 = 700
vii) 9100 + 5750
Round off to thousands
9100 round off to 9000
5750 round off to 6000
= 9000 + 6000 = 15000
viii) 6400 + 4900
Round off to thousands
6400 round off to 6000
4900 round off to 5000
= 6000 + 5000 = 11000
ix) 3731 - 1300
Round off to thousands
3731 round off to 4000
1300 round off to 1000
= 4000 - 1000 = 3000
x) 6885 - 4356
Round off to thousands
6885 round off to 7000
4356 round off to 4000
= 7000 - 4000 = 3000
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 + 4,317
b) 1,08,734 - 47,599
c) 8325 - 491
d) 4,89,348 - 48,365
Make four more such examples.
Answer:
a)
Rounding off to nearest hundreds
439 round off to 400
334 round off to 300
4317 round off to 4300
= 400 + 300 + 4300 = 5000
Rounding off to nearest tens
439 round off to 440
334 round off to 330
4317 round off to 4320
= 440 + 330 + 4320 = 5090
b)
Rounding off to nearest hundreds
1,08,734 round off to 108700
47,599 round off to 47600
= 108700 - 47600 = 61100
Rounding off to nearest tens
1,08,734 round off to 108730
47,599 round off to 47600
= 108730 - 47600 = 61130
c)
Rounding off to nearest hundreds
8325 round off to 8300
491 round off to 500
= 8300 - 500 = 7800
Rounding off to nearest tens
8325 round off to 8330
491 round off to 490
= 8330 - 490 = 7840
d)
Rounding off to nearest hundreds
489348 round off to 489300
48365 round off to 48400
= 489300 - 48400 = 440900
Rounding off to nearest tens
489348 round off to 489350
48365 round off to 48370
= 489350 - 48370 = 440980
Four examples of such are
i) 4899 + 662
Rounding off to nearest hundreds
4899 round off to 4900
662 round off to 700
= 4900 + 700 = 5600
Rounding off to nearest tens
4899 round off to 4900
662 round off to 660
= 4900 + 660 = 5560
ii) 770 - 310
Rounding off to nearest hundreds
770 round off to 800
310 round off to 300
= 800 - 300 = 400
Rounding off to nearest tens
770 round off to 770
310 round off to 310
= 770 - 310 = 460
iii) 63740 - 28759
Rounding off to nearest hundreds
63740 round off to 63700
28759 round off to 28600
= 63700 – 28600 = 35100
Rounding off to nearest tens
63740 round off to 63740
28759 round off to 28760
= 63740 - 28760 = 34980
iv) 8972 + 3548
Rounding off to nearest hundreds
8972 round off to 9000
3548 round off to 3500
= 9000 + 3500 = 12500
Rounding off to nearest tens
8972 round off to 8970
3548 round off to 3550
= 8970 + 3550 = 12520
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)
Rounding off by general rule
578 round off to 600
161 round off to 200
600 × 200 = 120000
b)
Rounding off by general rule
5281 round off to 5000
3491 round off to 3500
= 5000 × 3500 = 17500000
c)
Rounding off by general rule
1291 round off to 1300
592 round off to 600
= 1300 × 600 = 780000
d)
Rounding off by general rule
9250 round off to 9000
29 round off 30
= 9000 × 30 = 270000
Four examples of such are
i) 5340 × 89
Rounding off by general rule
5340 round off to 5000
89 round off 90
= 5000 × 90 = 450000
ii) 998 × 115
Rounding off by general rule
998 round off to 1000
115 round off to 120
= 1000 × 120 = 120000
iii) 4888 × 654
Rounding off by general rule
4888 round off to 4900
654 round off to 700
= 4900 × 700 = 3430000
iv) 382 x 1062
Rounding off by general rule
382 round off to 400
1062 round off to 1000
= 400 x 1000 = 400000
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