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.

Matching exercise

Match the items on the right to the items on the left.

STEP 1

STEP 2

STEP 3

STEP 4

Let the speed of her rowing in still water be ‘a’ and
speed of current be ‘b.’We know,

Relative speed of boat going upstream = a – b

Relative speed of boat going downstream = a + b

Given, Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours

⇒ a + b = 20/2 = 10 ---- (1)
and a – b = 4/2 = 2 ------ (2)

Adding eq1 and eq2

⇒ 2a = 12

⇒ a = 6 km/hr

Also, b = a – 2 = 4 km/hr

Therefore, her speed of rowing in still water is 6 km/h and the speed of the current is 4 km/h