4.5 is 0.9% of what number

500

Step-by-step explanation:

Lets make the unknown number the letter a

0.9% can also be shown as 0.9/100

so 0.9 of a = 4.5

x (0.9/100) = 4.5

multiply 0.9 by x

(0.9*a) / 100 = 4.5

multiply both sides by 100

0.9*a = 450

divide both sides by 0.9

a = 500

there you have it