Question

amber's mean mark in five tests is 80. Her marks on four tests are 68,81,74 and 89. work out her mark on the fifth test

Answer 1

Answer:

$\frac{68 + 81 + 74 + 89 + x}{5} = 80 \\ x = \frac{80 \times 5}{312} = \frac{360}{312} \\ = 1 \frac{2}{13}$

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