Question

Your quiz grades are 78, 72, 87, and 90. What score on the fifth quiz will make your average quiz grade at least 82?

Answer 1

Your scores are : 78, 72, 87 and 90
let fifth score = x
average = 82

$82= \frac{78+72+87+90+x}{5} \\ \\ \Rightarrow 82 \times 5=78+72+87+90+x\\ \\ \Rightarrow 410=327+x\\ \\ \Rightarrow 410-327=x\\ \\ \Rightarrow x=83$

So you should get atleast 83 to make your average atleast 82.

Answer 2

let fifth grade be x
average=a/n+b/n+c/n+.......n /n
so here average =82
applying formula
78/5+72/5+87/5+90/5+x/5 = 82
72+78+87+90+x=82*5
150+177+x=410
327+x=410
x=410-327
x=83