If the average (arithmetic mean) of x, y, and z is 7x and X ≠ 0, what is the ratio of x to the sum of y and z ?

1:21

1:20

1:6

6:1

20:1

##### 考题讲解

~$7x=\frac{x+y+z}{3}$~

~$\frac{x}{y+z}=\frac{1}{20}$~