10/400 = 2.5%
A value like 10/400, or 2.5%, can show up when a small part of a larger group has a certain feature. For example, it could describe 10 defective products out of 400, 10 rainy days in a 400-day record, or a small fee on a larger purchase.
To picture 2.5% quickly, think of 1 out of every 40 items. It is a small amount—about one quarter of 10%—so on a group of 100 things, it would look like only two or three items.
A common mistake is thinking that 10/400 is 10%, because people may focus on the numerator and overlook the much larger denominator. The denominator represents the whole group, so a value can have 10 parts in it and still be only a small percentage.
