Find the upper and lower bounds of the distance. It has been rounded to the nearest km so add and subtract 0.5 km to find the bounds.

52.5 km ≤ distance < 53.5 km

Two correct bounds [1]

Find the upper and lower bounds of the time. It has been rounded to the nearest 0.1 hour so add and subtract 0.05 hour to find the bounds.

2.65 hours ≤ time < 2.75 hours

All correct bounds [1]

$Speed = \frac{Distance}{Time} .$

To find the smallest possible speed you need to use the smallest possible distance and the largest possible time.

$\begin{array}{rcl} Lower bound for speed & = & \frac{52.5}{2.75} \\ = & \frac{210}{11} \\ = & 19.0909 . . . \end{array}$

[1]

To find the largest possible speed you need to use the largest possible distance and the smallest possible time.

$\begin{array}{rcl} Upper bound for speed & = & \frac{53.5}{2.65} \\ = & \frac{1070}{53} \\ = & 20.1886 . . . \end{array}$

[1]

Round your answers to 2 decimal places.

Lower bound = 19.09 km/h (2dp) [1]
Upper bound = 20.19 km/h (2dp) [1]

Rounding, Estimation and Bounds (CIE IGCSE Maths: Extended)

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