Give a rough estimate (by rounding off to nearest hundreds) and also a closer estimate (by rounding off to nearest tens)

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 + 4,317
(b) 1,08,734 – 47,599
(c) 8325 – 491
(d) 4,89,348 – 48,365

Solution

(a) By rounding off to nearest hundreds

439 rounds off to = 400
334 rounds off to = 300
4,317 rounds off to = 4,300
Estimated sum = 400 + 300 + 4,300 =  5,000

By rounding off to nearest tens

439 rounds off to = 440
334 rounds off to = 330
4,317 rounds off to = 4,320
Estimated sum = 440 + 330 + 4,320 =   5,090

(b) By rounding off to nearest hundreds

1,08,734  rounds off to = 1,08,700
47,599  rounds off to = 47,600
Estimated difference = 1,08,700 – 47,600 = 61,100

By rounding off to nearest tens

1,08,734  rounds off to = 1,08,730
47,599  rounds off to = 47,600
Estimated difference = 1,08,730 – 47,600 = 61,130

(c) By rounding off to nearest hundreds

8,325 rounds off to = 8,300
491 rounds off to = 500
Estimated difference  = 8,300 – 500 = 7,800

By rounding off to nearest tens

8,325 rounds off to = 8,330
491 rounds off to = 490
Estimated difference  = 8,330 – 490 = 7,840

(d) By rounding off to nearest hundreds

4,89,348 rounds off to = 4,89,300
48,365 rounds off to = 48,400
Estimated difference = 4,89,300 – 48,400  =  4,40,900

By rounding off to nearest tens

4,89,348 rounds off to = 4,89,350
48,365 rounds off to = 48,370
Estimated difference  = 4,89,350 – 48,370 = 4,40,980

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