A market researcher polled every tenth person who walks into a store. What type of sampling was used

Which of the following equations is equivalent to x/3-6/x=1

The distribution of a sample of the outside diameters of pvc pipes approximates a symmetrical, bell-shaped distribution. the arithmetic mean is 14.0 inches, and the standard deviation is 0.1 inches. about 68% of the outside diameters lie between what two amounts?

Solve the equation for x. 50(4x + 12) = 200