A boat travels 35km upstream and then back again in 4h & 48 min. If the speed in standing water is 15km/hr, what is the speed of the current?

Solution:

Let the speed of current = v kmph

35/(15-v)  + 35/(15+v) = 288/60

35[30]/(225 - v2)  = 288/60

225 - v2   = 35*1800/288 = 218.75

v2  = 6.25

v = 2.5 kmph