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**

^_^

## 2 comments:

check your math you are close but not quite there. Where do the sum of all datas come into play??

Edit for perfection.

Harbeck

Congrats on editing.

HArbeck

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