Class 6 Maths Knowing Our Numbers Estimating sum, difference and product

Estimating sum, difference and product

If a few numbers are to be added, subtracted or multiplied, the estimation can be obtained by estimating individual values. If the individual values are rounded off, then the calculations become simpler.

Addition

Subtraction

Multiplication

434 + 5253

ð  400 + 5300

ð  5700 (estimation)

ð  5687 (actual)

4525 - 832

ð  4500 - 800

ð  3700 (estimated)

ð  3693 (actual)

38 x 432

ð  40 x 430

ð  17200 (estimated)

ð  16416 (actual)

 

Problem: Estimate each of the following using general rule:

Expression

Rounding off criteria

Values after rounding off

Final Estimation

730 + 998

Rounding off to hundreds (rounding off value at tens place) for both figures

700 + 1000

1700

796 - 314

Rounding off to hundreds (rounding off value at tens place) for both figures

800 - 300

500

12,904 + 2,888

Rounding off to thousands (rounding off value at hundreds place) for both figures

13000 + 3000

16000

28,292 - 21,496

Rounding off to thousands (rounding off value at hundreds place) for both figures

28000 - 21000

7000

 

Problem: Estimate the products using general rule:

Expression

Rounding off criteria

Values after rounding off

Final Estimation

578 x 161

Rounding off to hundreds (rounding off value at tens place) for both figures

600 x 200

12000

5281 x 3491

Rounding off to thousands (rounding off value at hundreds place) for both figures

5000 x 3000

15000000

1291 x 592

Rounding off to hundreds (rounding off value at tens place) for both figures

1000 x 600

600000

9250 x 29

Rounding first number off to thousands (rounding off value at hundreds place) and second number off to tens (rounding off value at units place)

9000 x 30

270000

 

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