Pretest 2: Question 2

2. The mean mark on 4 tests is 78%. What mark is needed on the next test to increase the mean to 80%?

average of 4 test is 78%

4 x 78 = 312 or 78 + 78 + 78 + 78 = 312 = sum of all data

average of 5 test is 80%

5 x 80 = 400 or 78 + 78 + 78 + 78 + ? = 400 =sum of all data

the difference between the both is

400 - 312 = 88

meaning 78 + 78 + 78 + 78 + 88 = 400

^_^