Now, we know that Suki leaves 10 minutes before Tom and then Tom arrives 5 minutes before Suki. Therefore, we know that Tom takes 15 minutes (0.25 hr) less than Suki to travel 2km. Let us do this step by step.
Let’s Suki’s speed be ‘N km/h’. Then Tom’s speed must be ‘4N km/h’.
Let Suki’s total time be ‘T hrs’. Then Tom’s time would be ‘T-0.25 hrs”
Using distance = speed x time, we can get two equations:
a) NT = 2 km
b) 4N(T-0.25) = 2 km
If we manipulate the first equation to get N, we can see that N = 2/T. Substituting the expression of N into the second equation, we can get:
2/T x 4 (T-0.25) = 2km
8/T x (T-0.25) = 2
8 – 2/T = 2
8-2 = 2/T
6 = 2/T
Total time taken by Suki = 1/3 hours = 20 minutes
Suki’s speed = 2 ÷ 1/3 = 6 km/hr
Essentially, the question is asking us to calculate the distance she has travelled when Tom leaves. So, at the speed of 6 km/h after 10 minutes (1/6 hours), distance travelled by Suki:
Distance = 6 x 1/6 = 1 km