You are training for a marathon. On the first three days of training, you run for 2, 4, and 5 miles. How many miles should you run on the fourth day so that you run a mean of 4 miles per day?

Answer 1

x = miles run per day.

After four days mean is:

( x1 + x2 + x3 + x4 ) / 4 = 4

In this case x1 = 2 miles , x2 = 4 miles , x3 = 5 miles so:

( x1 + x2 + x3 + x4 ) / 4 = 4

( 2 + 4 + 5 + x4 ) / 4 = 4

( 11 + x4 ) / 4 = 4

Multiply both sides by 4

11 + x4 = 16

Subtract 11 to both sides.

x4 = 5 miles

Check result:

( x1 + x2 + x3 + x4 ) / 4 = ( 2 + 4 + 5 + 5 ) / 4 = 16 / 4 = 4

Answer 2

oh ok thanks so much