Question

If a boatman can row upstream at 10 km/h and downstream at 12 km/h, then find the ratio of the speed of the boat in still water and the speed of the current.

• A. 2 : 11
• B. 11 : 1
• C. 11 : 2
• D. 1 : 11

Answer 1

Answer:

B. 11 : 1

Let:

• Speed of boat in still water = (b)

• Speed of current = (c)

Given:
$b - c = 10 \quad (\text{upstream})$
$b + c = 12 \quad (\text{downstream})$
Add equations

$(b - c) + (b + c) = 10 + 12$
$2b = 22 \Rightarrow b = 11$
Substitute to find (c)

$11 + c = 12 \Rightarrow c = 1$
Ratio

$b : c = 11 : 1$