This is a percentage decrease, since the number gets smaller. To calculate percentage decrease, you use the formula ((y1 - y2) / y1) * 100. y1 = 23, y2 = 18. Plug in the values and solve.
((23 - 18)/23) * 100.
(5/23) * 100.
(0.2174) * 100
21.74
So your answer is 21.74%
