Step 1:
Let us first find the decrease in amount.
Decrease in amount = 150 -120 = $30
Step 2:
Now let us find the ratio of decrease in price to original price.
So the ratio is 1/5 or in decimal its 0.2.
Step 3:
To find percentage decrease we change this decimal number 0.2 two places to the right side, so it becomes 20 %
The price decreased by 20%