Checking and securing understanding of estimating through rounding | Maths

Starter quiz

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

'approximately' ✓
Round 780 257 to the nearest ten thousand.

'780 000' ✓
Round 123.408 to 2 decimal places.

'123.41' ✓
Round 0.01872 to 2 significant figures.

'0.019' ✓
Truncate 74 283 to 2 significant figures.

'74 000' ✓
Truncate 0.02078 to 3 significant figures.

0.020 ✓

0.0207

0.0208

0.021

When estimating calculations round each value to 1 ______ figure.

'significant' ✓
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

£50 × 5 + £30

£40 × 5 + £30

£50 × 6 + £30 ✓

£50 × 6 + £32

£48 × 6 + £30
Estimate the value of $7.236\times38.4\over1.704$

'140' ✓
Will the estimation of 45.87 × 763 be an overestimate or underestimate?

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

'400 cm' ✓
Estimate the area of a circle with a diameter of 12.8 cm.

'<Math>108 cm^2</Math>' ✓

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Rounding to 1 significant figure allows quick estimation with the magnitude of the estimation being close.
The estimation will be closer to the true answer the less rounding you do.
Estimating through rounding is meant to be quick and easy, taking too long defeats the purpose.

Assuming all zero digits are not significant.

Relate significance back to the communication of accuracy and that some digits are significant as they preserve the place value of other digits.

Estimate - A quick estimate for a calculation is obtained from using approximate values, often rounded to 1 significant figure.
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.
Overestimate - An estimate for a calculation which is greater than the exact answer.
Underestimate - An estimate for a calculation which is less than the exact answer.