Isabella has completed four assessment tasks, each marked out of 100, giving her a mean of 71%. She wants to increase her mean to 75% after the trial. Which of the following below will calculate the mark (x) she needs to achieve in the next assessment task?
a. $$x=\frac{71+75}{2}$$
b. $$x=\frac{71+75}{2}$$
c. $$75=\frac{71\times4+x}{2}$$
d. $$75=\frac{71\times4+x}{5}$$
the total of 4 tests with an average of 71 will be 71 × 4
then the 5th test is x
so the total of all five tests will be 71 × 4 + x
to find the average of these 5 tests, divide by 5
since the average is to be 75 then $$75=\frac{71\times4+x}{5}$$
D