Let X = one number

Let Y = the other number

"The sum of two numbers is 24" gives us:

X+Y=24

"One number is 2 times as large as the other" gives us:

X=2Y

Substitute 2Y from the second equation in place of X in the first equation:

2Y+Y=24

3Y=24

Y=8

Plug that in for Y in the second equation:

X=2(8)

X=16

So our numbers are 16 and 8.