Question

Fran swims at a speed of 2.8 mph in still water. The Lazy River flows at a speed of 0.8 mph. How long will it take Fran to swim 4 mi​ upstream? 4 mi​ downstream?

Answer 1

1.49 hrs or 1 hr and 30 minutes approximately

Explanation:

if fran go 2.8m up then the river flow at a rate of 0.8m; the since we are taking the speed of fran and river to be constant. the ratio between their speed will always remain constant. that is if 0.8/2.8 = 0.286≈ this will be always constant.

so if he go up 4m then the horizontal length has to be 1.143 because 1.143/4 = 0.286.

now we find the distance between frans initial positon and final position. to find it we use pythagoras theorem.

`√((4^2 + 1.143^2)) =4.160 miles`

to find the time divide distance traveled by speed;

4.160/2.8 = 1.49 hrs