Question

ANSWER ASAP

A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes for the boat to go upstream the same 8 miles. Find the speed of the current. 4 mph 24 mph 16 mph 20 mph (this is on gradpoint)

Answer 1

the correct answer is C = 4 mph

Answer 2

4 mph

Explanation:

Let x is the speed of the current

Let y is the speed of the motorboat

As we know: speed = distance / time

It takes 30 minutes (= 1/2 hours) for the boat to go upstream the same 8 miles

y - x = 8 /
`(1)/(2)` mph

<=> y - x = 16 mph (1)

<=> x = y -16 mph

A motorboat can go 8 miles downstream on a river in 20 minutes (= 1/3 hour)

y + x = 8 /
`(1)/(3)` mph

<=> y + x = 24 mph (2)

Solve the system of equation (1) and (2), we have:

y + x = 24 mph

<=> y + y -16 = 24 mph

<=> 2y = 40 mph

<=> y = 20 mph

=> x = 20 -16 = 4 mph

So the speed of the current is 4 mph