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Question -

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) 4853 + 662

Rounding off to nearest hundreds

4853 + 662 = 4800 + 700

= 5500

Rounding off to nearest tens

4853 + 662 = 4850 + 660

= 5510


(ii) 775 – 390

Rounding off to nearest hundreds

775 – 390 = 800 – 400

= 400

Rounding off to nearest tens

775 – 390 = 780 – 400

= 380


(iii) 6375 – 2875

Rounding off to nearest hundreds

6375 – 2875 = 6400 – 2900

= 3500

Rounding off to nearest tens

6375 – 2875 = 6380 – 2880

= 3500


(iv) 8246 – 6312

Rounding off to nearest hundreds

8246 – 6312 = 8200 – 6300

= 1900

Rounding off to nearest tens

8246 – 6312 = 8240 – 6310

= 1930

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