Question

Fran swims at a speed of 2.8 mph in still water. The Lazy River flows at a speed of 0.6 mph. How long will it take Fran to swim 2.2 mi? upstream? 2.2 mi? downstream?

Answer 1

1. Upstream Time: 1 hour (or 60 minutes)

2. Downstream Time: 0.65 hour (or 39 minutes)

Explanation:

The time it will take goes by the distance formula:

`D=RT`, where D is the distance, R is the rate (speed), and T is the time.

For Upstream, you are going against the current, so your still water speed slows down. So upstream rate is still water rate - stream rate. So 2.8 - 0.6 = 2.2mph

Time it will take him to swim 2.2 miles, is:

`D=RT\\2.2=2.2(T)\\T=(2.2)/(2.2)=1`

So, 1 hour

For Downstream, you are going with the current, so your still water speed increases. So downstream rate is still water rate + stream rate. So 2.8 + 0.6 = 3.4 mph

Time it will take him to swim 2.2 miles, is:

`D=RT\\2.2=3.4(T)\\T=(2.2)/(3.4)=0.65`

So, 0.65 hours (or 0.65*60=39 minutes)