Hello from MrBillDoesMath!
Answer:
Choice C [16,100]
Discussion:
Let "x" be the score needed on the 5th exam to achieve an average score >= 60. Then
(50 + 90 + 66 + 78 + x)/5 >= 60 => (multiply both sides by 5)
(50 + 90 +66 + 78) + x >= 60*5 = 300 =>
(284) + x >= 300 =>
x >= 300 - 284 = 16.
As x is a percent, x <= 100, so the interval is [16, 100], which is Choice C.
Thank you,
MrB
