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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 + 4317 (b) 108734 – 47599 (c) 8325 – 491 (d) 489348 – 48365
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) 108734 – 47599
Rounding off to nearest hundreds
108734 – 47599 = 108700 – 47600
= 61100
Rounding off to nearest tens
108734 – 47599 = 108730 – 47600
= 61130
(c) 8325 – 491
Rounding off to nearest hundreds
8325 – 491 = 8300 – 500
= 7800
Rounding off to nearest tens
8325 – 491 = 8330 – 490
= 7840
(d) 489348 – 48365
Rounding off to nearest hundreds
489348 – 48365 = 489300 – 48400
= 440900
Rounding off to nearest tens
489348 – 48365 = 489350 – 48370
= 440980
Four more examples are as follows
(i) 2343 + 1692
Rounding off to nearest hundreds
2343 + 1692
= 2300 + 1700
= 4000
Rounding off to nearest tens
2343 + 1692 = 2340 + 1690= 4030
(ii) 9086 – 1390
Rounding off to nearest hundreds
10000 – 1400 = 8600
= 8600
Rounding off to nearest tens
9086– 1390 = 9090 – 1390
= 7700
(iii) 1234 – 346
Rounding off to nearest hundreds
1234 – 346= 1200 – 300= 900
Rounding off to nearest tens
1234 – 346= 1230 – 350= 880
(iv) 2251+7654
Rounding off to nearest hundreds
2251+7654 = 2300+7700
= 10000
Rounding off to nearest tens
2251+7654 = 2250+7650
= 9900