Boat running upstream takes 640 min to cover a certain distance , while it…
2024
Boat running upstream takes 640 min to cover a certain distance , while it takes 280 min to cover the same distance running down stream . What is the ratio between the speed of the boat and speed of the boat and speed of water current respectively ?
- A.
23:7
- B.
22:9
- C.
23:8
- D.
23:9
Attempted by 4 students.
Show answer & explanation
Correct answer: D
Answer: 23 : 9
Let the speed of the boat be x and the speed of the current be y.
Time upstream: d/(x - y) = 640, so d = 640(x - y).
Time downstream: d/(x + y) = 280, so d = 280(x + y).
Equate the two expressions for d: 640(x - y) = 280(x + y). Divide by 40 to simplify: 16(x - y) = 7(x + y).
Expand and simplify: 16x - 16y = 7x + 7y ⇒ 9x = 23y ⇒ x/y = 23/9.
Therefore the ratio of the boat's speed to the current's speed is 23:9.