A quick estimate for a calculation is obtained from using approximate values, often rounded to 1 significant figure.

Significant figures are the digits in a number that contribute to the accuracy of the number. The first significant figure is the first non-zero digit.

An estimate for a calculation which is greater than the exact answer.

An estimate for a calculation which is less than the exact answer.

Checking and securing understanding of estimating through rounding

Maths

In the prior unit, pupils learnt how to round to a given number of decimal places or significant figures and explored the effect of using rounded numbers for calculations. In this unit, pupils will investigate the bounds and perform calculations to determine a best/worst case scenario.

This unit explores the impact of upper and lower bounds on additive and multiplicative calculations.

Rounding, estimation and bounds

When estimating calculations round each value to 1 {{ }} figure. 

Choose the correct calculation to estimate the cost of hiring a plumber for 5.75 hours, where the total cost = £48 × number of hours + £32 

Estimate the value of $$7.236\times38.4\over1.704$$

Will the estimation of 45.87 × 763 be an overestimate or underestimate?

Estimate the total length of 23 bricks if each brick measures 21.5 cm.

Estimate the area of a circle with a diameter of 12.8 cm.

Rounding means to change a number into another number that is {{ }} the same value but is easier to work with.

Round 780 257 to the nearest ten thousand.

Truncate 74 283 to 2 significant figures.

Truncate 0.02078 to 3 significant figures.

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