Question

Formulate the following problems as a pair of equations, and hence find their solutions:

Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours. Find her speed of rowing in still water and the speed of the current

Answer 1

Let the speed of Ritu in still water and the speed of stream be x km/h and y km/h respectively.

Speed of Ritu while rowing

Upstream = (x - y) km/h

Downstream = (x + y) km/h

According to question,

2(x + y) = 20

⇒ x + y = 10 ... (i)

2(x - y) = 4

⇒ x - y = 2 ... (ii)

Adding equation (i) and (ii), we get

2x = 12 ⇒ x = 6

Putting this equation in (i), we get

y = 4

Hence, Ritu's speed in still water is 6 km/h and the speed of the current is 4 km/h.