He donated 18 books per month. you first finds the difference of the books then do use the number of books by the number of months (in this case it was 5 months)
The student would have to score 100% on their next test to brung their average up to 90. Here is why;
90+84+86=260
(260+?)/4=90
(260+100)/4=90
360/4=90
This is done to get the mean (or average) of a group of numbers by adding all the numbers and dividing by the amount of numbers you added together. Here it is divided by 4 because of the three tests he has taken and the test he will take.
I believe that the answer is C, I don't know if it is addition or multiplication, but if is is addition, it would be 146, C
The rectangle looks like
A —— B
D —— C
so AB = 84
BC = 63
AD = 63
CD = 84
