Answer:
She must score 103 on her next test.
Step-by-step 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
[tex]\text{Her average score}=\frac{\text{Total sum of scores}}{\text{Number of tests}}[/tex]
[tex]=\frac{347 + x}{5}[/tex]
According to the question,
Her average score = 90
[tex]\implies \frac{347 + x}{5}=90[/tex]
[tex]347+x=450[/tex]
[tex]x=103[/tex]
Hence, she must score 103 on her next test.
