Question

A motorboat leaves a harbor and travels at an average speed of 15 mph

toward an island. The average speed on the return trip was 10 mph. How far was the
island from the harbor if the total trip took 5 hours?

Answer 1

30 miles

Explanation:

We know

D = RT

Where

D is the distance

R is the rate

T is the time

Towards Island:

R = 15

Let time be x

So, we can write:

D = 15x

Return from Island:

R = 10

Let time be y

So, we can write:

D = 10y

Also, total time is 5 hours, so we can write:

x + y = 5 [equation 2]

Now, since the distance for both legs of the journey is equal, we can write:

Distance 1 = Distance 2

15x = 10y

Now we replace this equation with equation 2, so we get:

Equation 2: x + y = 5 or x = 5 - y

15x = 10y

15(5 - y) = 10y

75 - 15y = 10y

75 = 25y

y = 75/25

y = 3

Distance 2 = D = 10y

Replacing y with 3, we get:

D = 10y

D = 10(3)

D = 30

So, the distance to island is 30 miles