Let T, K, and B be the ages of Tom, Kathy, and Baba when Tom came to London. Then K= T+ B.

From that K- B= T. That is, Kathy is T years older than Baba and so "Kathy was as old as Baba was when Tom came to London" T years ago. T years ago, Tom's age was T- T= 0!

Let v be the speed of the river relative to its banks, and let V be the speed of the swimmer relative to the river. The swimmer's speed, relative to the banks of the river, swimming upstream is V- v. The swimmer's speed relative to the banks of the river, swimming downstream is v+ V. All speeds are in km/min. Let T be the time the swimmer swam2)A swimmer was swimming upstream River A. Near the Bridge R he lost

A ball. After swimming 20 min more upstream he noticed his loss and

swam back to find the ball; he reached it near the Bridge S. Find the

velocity of current at River A if the distance between these two bridges

is 2 km. (Ans: 3 km/h).downstreamafter the ball. The ball was floating downstream for T+ 20 minutes and so went a distance v(T+ 20)= 2 km. The swimmer went 20(V- v) km upstream and then T(v+ V) km downstream so we have T(v+ V)- 20(V- v)= 2. Tv+ TV- 20V+ 20v= V(T- 20)+ v(T+ 20)= V(T- 20)+ 2= 2km. That is V(T- 20)= 0 so either V= 0 (the swimmer was just floating in the river himself and so was always beside the ball) or T= 20.

How far has the swimmer travelled before he turned back to prick uo the ball.

A schematic diagram can be helpful.