A boat makes a round trip across a lake in 4 hours. Going across, the boat averages 10 km/h. Returning, it averages 15 km/h. How far is it across the lake?

Question

How would I set this up?

Answer 1

distance/speed = time

 

distance there = distance back

 

Let;

x = distance

 

x/10 + x/15 = 4

 

multiply by 1 to get a common denominator

 

(3/3)*(x/10) + (2/2)*(x/15) = (30/30)*(4/1)

 

3x/30 + 2x/30 = 120/30

 

5x = 120

 

x = 24 km