What is 90 decreased by 40%?

Because it's decreasing, you use the formula (1-x/100)y with x the percentage decreased which is here 40, and y the number decreased which is here 90
So we get
(1-40/100) * 90
(100/100 - 40/100) * 90
60/100 * 90 
5400/100
54 
So 90 decreased by 40% is 54
Hope this Helps :)