I hope I am reading the problem right: The price of a mountain bike increased by 20% in the past year. The value is $150. What was the value of the mountain bike last year?
Let's simplify this. One year, there was this radical mountain bike that used to have an unsaid price, x. That year, that price of x increased by 20% more than it was before, or 120% times the original value. Because of that, it's now $150.
We can equation this.
1.20x = 150
x = 150/1.2
x = 125
The bike, I believe, cost $125 last year. Hope this helps!