The number increased by 40%. By how many percent you need to reduce the received number to get this number.

Suppose the original number is unknown – x.
If it was increased by 40%, then it became x * 140% or x * 1.4 = 1.4x.
Let’s compose the proportion in which we write down the difference between the original number and the new one.
1.4x-x = 0.4x
0.4x / 1.4x = 0.285
From this it follows that the number needs to be reduced by 28.5 percent.
For example, the solution looks like this.
There was a number 100, it was increased by 40%
100 + 100 * 40% = 100 + 40 = 140.
40/140 = 0.285 or 28.5%
Answer. It is necessary to reduce the new number by 28.5%