Impossible and I mean it
A girl walks from her house to the pool at 6 km/hr. The distance between her pool and her house is unknown. A boy lives somewhere and reaches the pool exactly when she reaches.
The next day, she goes to the library which is located after the pool, 20 minutes late. When she reaches the pool, the boy is not there yet when she reaches the library he is there (exactly when she is there). The distance between the pool and the library is 3 km.
Find out the speed of the boy.
Here is a diagram which shows the girl's journey; to help you:
Notes and assumptions:
(1) The girl and boy are travelling at constant speed.
(2) On both days their speeds are same and constant i.e. On the second day, the girl is travelling at 6 km/hr
(3) Both the girl and the boy start their journey from the same points (their respective houses) on both days.
(4) The girl and the boy start their journeys at the same time on the first day (e.g. at 8 am) and the boy starts his journey 20 minutes later than the girl on the second day
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1 solution
This is level 5? ?? Anyway, we will be assuming this boy's house lies on the same line as the girl's house, pool and the library are. With that in mind, let the distance between the two houses, the distance between the girl's house and the pool and the speed of the boy be z km, x km and y km/h respectively. x/6 = (x+z)/y, 20 mins = 1/3h = 2/6h, (x+3)/6 = (x+z+3)/y - 2/6, (x+1)/6 = (x+z+3)/y, 1/6 = 3/y, 3/18 = 3/y, 18 = y.