Arithmetic 65324

Martin has an arithmetic average of 2.8 out of five history grades. If he only gets one from now, how many ones would he have to get at least so that the arithmetic mean of his history grades is less than 2?

Correct answer:

n =  4

Step-by-step explanation:

$$\begin{gathered} m=5 \\ \frac{m\cdot 2.8+n\cdot 1}{m+n}=2 \\ 5\cdot 2.8+1\cdot n=2\cdot (5+n) \\ n=4 \\ n=\frac{4}{1}=4 \\ n=4 \end{gathered}$$

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