Question

Davids scores on the first three of four 100-point math tests were 86, 92, and 89. What score does he need on his fourth math test to ensure an average score of at least 90?
A. x > 89

B. x > 93

C. x > 78

D. x > 90

Answer 1

So the problem wants to compute what could David should score in the fourth math test to ensure an average score of at least 90. So base on the score the possible total of the four score must be 360 to make their average of minimum of 90 so the answer would be letter B. X>93

Answer 2

Answer:

Step-by-step explanation:

Davids scores on the first three of four 100-point math tests were 86, 92, and 89.

Let x be the score he need on his fourth math test.

Average of scores of four test is

$Average=\frac{\sum x}{n}$

$Average=\frac{86+92+89+x}{4}$

$Average=\frac{267+x}{4}$

It is given that average score of at least 90. It means average must be greater than 90.

$Average>90$

$\frac{267+x}{4}>90$

Multiply 4 on both the sides.

$267+x>360$

Subtract 267 from both the sides.

$x>360-267$

$x>93$

Therefore the correct option is B.