Question

In Mei Lin's school, her science teacher gives tests that are marked out of 100. Mei Lin has a average of 60 marks on her first four Science tests. On the fifth test she got 80 marks. What is the average of Mei Lin's marks in Science after all five tests?​

Answer 1

the answer is attached to the picture

Answer 2

Average of five tests is 64.

Step-by-step explanation:

Given that,

Average of first four test = 60

Marks of fifth test = 80

Let the marks of first 4 test be x₁ , x₂, x₃ and x₄

=> According to the condition given,

Average of first four tests = 60

$\frac{x_{1} + x_{2} + x_{3} + x_{4}}{4} = 60\\\\ x_{1} +x_{2} +x_{3} +x_{4} = 240---(i)$

=> Average of five test will be ,

$\frac{Sum \ of \ marks \ of \ all \ tests}{Total \ number \ of \ tests}$

$\frac{ x_{1} +x_{2} +x_{3} +x_{4} + 80}{5}$

Susbtituiting the value of  $x_{1} +x_{2} +x_{3} +x_{4}$ from equation (i)

$\frac{240+80}{5}\\\\ \frac{320}{5}\\\\ 64$

=> The average of five tests is 64.