The mean of 5 numbers is 18. If one number is excluded, their mean is 16. Find the excluded number.
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$\displaystyle \frac{x_1+x_2+x_3+x_4+x_5}{5} = 18\implies x_1+x_2+x_3+x_4+x_5 = 90$ $\displaystyle \frac{x_1+x_2+x_3+x_4}{4} = 16\implies x_1+x_2+x_3+x_4 = 64$ $\displaystyle x_5=90-64 $
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