Maths worded problem on Lower bounds

Question

Sophie estimated that the distance between Bristol and Newcastle is about 290 miles and that her average driving speed would be 60 mph.
She estimated the distance to the nearest 10 miles and the speed to the nearest 10mph.
Calculate the lower bound of the time the journey should take.
Give your answer in hours and minutes.
Give your answer to the nearest minute.

Answer 1

The lowest bound is the shortest time the journey could take within her estimate. Her estimates are:

 

distance = (290 ± 10) miles

speed = (60 ± 10) mph

 

To get the lowest bound, we assume the shortest possible distance (280 miles) and the fastest possible speed (70 mph). Since

speed = distance ÷ time, this implies time = distance ÷ speed, which gives the answer.