Question

Mallory wants to run an average of 4 miles per day during the week (Monday
through Friday). Use the table below to find the number of miles x she needs to
run on Friday so that the mean number of miles ran per day is 4. PLEASE HELP

Answer 1

To find mean(average): add all terms and divide by n (number of terms or days of the week)
(Monday+tuesday+Wednesday+thursday+friday)/5= mean(average)

(4+4.5+0+2.5+x)/5=4 (she wants to have a mean of 4 miles per day)
MULTIPLY BOTH SIDES BY 5

5*(4+4.5+0+2.5+x)/5=4*5

(4+4.5+0+2.5+x)=20
ADD WHAT YOU KNOW

(11+x)=20
SUBTRACT 11 FROM BOTH SIDES

(11+x)-11=20-11
(x)=9
So she needs to run 9 miles on friday to have a mean of 4 miles per day