To determine the original amount before a percentage increase, you can divide the increased amount by $1$ plus the percentage increase.

When you have an amount that has undergone a percentage increase, you can reverse the process to uncover the original amount. Let’s illustrate this with an example. Suppose you know that an item now costs £120 after experiencing a $20\%$ increase. To find the original price, you must recognize that £120 corresponds to $120\%$ of the original price (which is $100\%$ plus $20\%$).

First, convert the percentage increase into a decimal format. For a $20\%$ increase, you convert $20\%$ to $0.20$. Adding this to $1$ accounts for the original $100\%$, resulting in $1.20$. This indicates that the new amount is $1.20$ times the original amount.

Next, take the increased amount (£120 in this case) and divide it by $1.20$. This gives you the calculation:

Calculating this yields:

Thus, the original amount before the increase was £100.

This method is applicable to any percentage increase. Simply remember to convert the percentage to a decimal, add it to $1$, and then divide the increased amount by this result. This will enable you to find the original amount prior to the percentage increase being applied.