solve x in the following proportion 4:10=x:40?

4 x 10 =40 so
4 x 4 = 16
16:40

x = 16

the the colon may be regarded as a division symbol

x = 16.

x = 16

Thanks for the two points, Jeff J.

Multiply 4 and 40 which gives you 160, then divide by 10 which gives you 16.

16 : 40 = x : 40
x = 16

Take the terms as fractions:
4/10 and x/40 (cross multiply and you'll get...)
10x = 160 (divide both sides by 10 to cancel 10 in eqaution 10x)

YOU'LL GET:

16

4:10 = x:40
4/10 = x/40
4 = 10(x/40)
4 = 10x/40
4 = x/4
x = 4(4)
x = 16

x=16

X = 16