Question

If the mean of x and 4x is 10, the x = ?

Answer 1

$\dfrac{x+4x}{2}=10\\\\\dfrac{5x}{2}=10\ \ \ \ |multiply\ both\ sides\ by\ 2\\\\5x=20\ \ \ |divide\ both\ sides\ by\ 5\\\\\boxed{x=4}$

Answer 2

Divide the 10 by 4, which makes the x be 2.5. You can check it by multiplying 4 by 2.5, which will give you 10.