The correct equation that represents the expression "The number 24 is what percent of the number 40?" is as shown below;
The the unknown number in percent be 'x'
x percent of number 40 is expressed as;
x% of 40
x/100 of 40
If 24 is equal to the expression above, then the final equation will be expressed as;
24 = x/100 of 40
24 = 40x/100
24 = 0.4x
Rearrange
0.4x = 24
Hence the correct equation used to solve the problem is 0.4x = 24