Abicycle was originally sold for $400 was on sale for $320. what percent was the bike marked down?

100% of the price = $400
x % of the price = $320
we need to find x

using a proportion
100 : 400 = x : 320
100 * 320 = 400 * x
32000 = 400x
x = 32000 / 400
x = 80

That means the new price is 80% of the previous price.
100% - 80% = 20%
and based on this we can make a conclusion that the discount was 20%

I hope it is clear to you, feel free to ask anything about it :)

20% because 20% is $60 and you can keep adding $60 4 more times so there's 5 of $60

What’s the equation you are trying to solve to get x?