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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.
Solution: (a) 730+ 998
Round off to hundreds
730 rounds off = 700
998 rounds off to = 1000
Estimated sum = 1700
Hence, by estimate 730 + 998 = 700 + 1000 =1700
(b) 796 - 314
Round off to hundreds
796 rounds off to = 800
314 rounds off to = 300
Estimated difference = 500
Hence, by estimate 796 - 314 = 800 - 300 = 500
(c) 12904 + 2888
Round off to thousands
12904 rounds off to = 13000
2888 rounds off to = 3000
Estimated sum = 16000
Hence, by estimate 12904 + 2888 = 13000 + 3000 = 16000
d) 28292 - 21496
Round off to thousands
28292 round off to = 28000
21496 round off to = 21000
Estimated difference = 7000
Hence, by estimate 28292 - 21496=28000 - 21000 = 7000
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.
Solution: (a) 439+334+4317
Rounding off to nearest hundreds
439 round off to = 400
334 round off to = 300
4317 round off to = 4300
Estimated sum = 400 + 300 + 4300 = 5000
Rounding off to nearest tens
439 round off to = 440
334 round off to = 330
4317 round off to = 4320
Estimated sum = 440+ 330 + 4320 = 5090
(b) 108734 - 47599
Rounding off to nearest hundreds
108734 round off to = 108700
47599 round off to = 47600
Estimated difference = 108700 - 47600 = 61100
Rounding off to nearest tens
108734 round off to = 108730
47599 round off to = 47600
Estimated difference = 108730 - 47600 = 61130
(c) 8325 – 491
Rounding off to nearest hundreds
8325 round off to = 8300
491 round off to = 500
Estimated difference = 8300 - 500 = 7800
Rounding off to nearest tens
8325 round off to = 8330
491 round off to = 490
Estimated difference = 8330 - 490 = 7840
(d) 489348 - 48365
Rounding off to nearest hundreds
489348 round off to = 489300
48365 round off to = 48400
Estimated difference = 489300 - 48400 = 440900
Rounding off to nearest tens
489348 round off to = 489350
48365 round off to = 48370
Estimated difference = 489350 - 48370 = 440980
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.
Solution: (a) 578 x 161
578 rounds off to = 600
161 rounds off to = 200
Product = 600 x 200 = 1,20,000
(b) 5281 x 3491
5281 rounds of to = 5,000
3491 rounds off to = 3,500
Product = 5,000 x 3,500 = 1,75,00,000
(c) 1291 × 592
1291 rounds off to = 1300
592 rounds off to = 600
Product = 1300 x 600 = 7,80,000
(d) 9250 x 29
9250 rounds off to = 10,000
29 rounds off to = 30
Product = 10,000 x 30 = 3,00.000
Answer:
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