18/90 = 20%
A value like 20% can show up in everyday life as a sale discount, a tip, or the battery left on a phone. For example, a 20% discount means the price is reduced by about one-fifth.
To picture it quickly, imagine 100 equal squares with 20 shaded, or a group of five equal parts with one part highlighted. That makes it easy to think of as roughly one out of every five.
A common mix-up is treating 20% as the same amount no matter what the total is. A 20% discount saves much more on a $100 item than on a $10 item.
