Question

A long distance runner does a first lap around a track in exactly 50 seconds. as she tires, each subsequent lap takes 20% longer than the previous one. how long does she take to run 3 laps?

Answer 1

new percentage=100+20=120%
1st lap= 120%of 50= 60
2nd lap= 120% of 60= 72
3rd lap= 120% of 72= 86.4 second

Answer 2

The first lap takes 50 seconds. Each subsequent lap takes 20% longer than the previous one.

So we can write the time taken to run the
`n`the lap is
`T_n=(1+(20)/(100))T_(n-1)= 1.2T_(n-1),n=2,3,4,...`.

So we can write,
`image`

So the time taken to run 3 laps is

`50+60+72=182\;seconds`