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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