Coaching Centre
Estimating and rounding
Rounding whole numbers to the nearest 10, 100 or 1000, rounding to the leading digit, and estimating answers to check calculations.
Rounding
Round $68\,451$ to (a) the nearest hundred and (b) the nearest thousand.
Estimating
To estimate, round each number to its leading digit (the first non-zero digit) and then calculate.
Estimate $4782 \times 29$.
Round $68\,451$ to the nearest hundred.
The tens digit is $5$.
Round $68\,451$ to the nearest thousand.
The hundreds digit is $4$.
Round $3449$ to the nearest thousand.
Look only at the hundreds digit, $4$.
Round $395$ to the nearest ten.
$395$ rounds up to $400$.
The best estimate of $4782 \times 29$ is:
$5000 \times 30$.
Estimate $812 \div 19$.
$800 \div 20 = 40$.
Round $1\,549\,999$ to the nearest million.
The hundred-thousands digit is $5$.
A calculator shows $612 \times 48 = 2937.6$. Is it reasonable?
$600 \times 50 = 30\,000$. A decimal point was misplaced.
New numbers every time. Keep going until you get five in a row.