Given :
She run 3 miles 1 st day .
She run 5 miles 2 nd day .
Then she runs 7 miles per day .
To Find :
If she total runs 99 miles , for how many days has Carla been running 7 miles.
Solution :
The relation between total miles run and number of days she run 7 miles is :
[tex]D=7n+3+5[/tex]
Putting , D = 99 miles , we get :
[tex]7n+8=99\\\\n=\dfrac{91}{7}\\\\n=13[/tex]
From 13 days she is running 7 miles in a day .
