When more than one value in a calculation has been rounded, the upper or lower bounds for each value should be used in the calculation to find the greatest or least possible values that the calculation can take.
A bag of flour has a mass of 1500 g (to the nearest 10 g). Find the upper bound for the mass of 10 bags of flour.
The upper bound of 1500 g rounded to the nearest 10 g is 1505 g. The upper bound for 10 bags of flour is therefore ( = 15.05 kg).
Jack is 1.8 m tall (rounded to the nearest 10 cm). Ella is 1.63 m tall (rounded to the nearest cm). What is the smallest possible difference in their heights?
To find the smallest difference, we need to use the lower bound for Jack’s height and the upper bound for Ella’s height. The lower bound of 1.8 m (rounded to the nearest 10 cm) is 1.75 m. The upper bound of 1.63 m (rounded to the nearest cm) is 1.635 m.
A piece of A4 paper is 21.1 cm by 29.7 cm measured to the nearest 0.1cm. What are the lower and upper bounds of its area, in square centimetres, correct to 1 dp?
This problem requires the biggest and smallest areas possible. What are the upper and lower bounds of the measurements and how should they be combined to achieve the correct outcomes?
In this example, the maximum area is found by multiplying the two upper bounds. The minimum area is found by multiplying the two lower bounds.
The following rules help to decide which bounds to use when doing combinations and calculations.
A = 34 cm to the nearest cm.
B = 11.2 cm to 1 decimal place.
C = 200 cm to 1 significant figure.