We are given that:
>perfect score- 100
>number of questions of the test- 25
>worth of each question- 4 points
>Fred's score- 84
Let us say that n- number of questions Fred answered wrong
The solution:
let us solve for n
>division sentence: (100 ÷ 4 ) - ( 84 ÷ 4 ) = n
(100 ÷ 4 ) - ( 84 ÷ 4 ) = n
25 - 21 = n
4= n
Therefore Fred answered 4 test questions incorrectly.