Question

Rosa's test scores are 78, 92, 88, and 89. what must she score on her next test to have an average of 90?

Answer 1

Rosa must score a 103 on her next test to create an average of 90

Answer 2

She must score 103 on her next test.

Explanation:

Given,

The scores in four tests are,

78, 92, 88, and 89

Number of tests = 5,

Let x be the score on her next test or fifth test

So, the sum of scores in five tests = 78 + 92 + 88 + 89 + x = 347 + x

`\text{Her average score}=\frac{\text{Total sum of scores}}{\text{Number of tests}}`

`=(347 + x)/(5)`

According to the question,

Her average score = 90

`\implies (347 + x)/(5)=90`

`347+x=450`

`x=103`

Hence, she must score 103 on her next test.