Question

The mean of a particular set of 7 numbers is 4. Six of the numbers in the set are known: 1,2,2,5,7,and 8.

Answer 1

$\dfrac{1+2+2+5+7+8+x}{7}=4\\ \dfrac{25+x}{7}=4\\ 25+x=28\\ \boxed{x=3}$