It's y=kx. But 'k' is any constant. So my 'k' can easily be 1/(your k). The key is that when 'x' or 'y' increases by some factor, the other one also increases, by some constant multiple of the same factor. If so, then they're proportional.
15% off
15% off of 50
notice that 50 is 1/2 of hundred
15% of 100 is 15
therefor
15% of 50 is 15/2=7.5
that is discount
50-7.5=42.5
new price=$42.5
Now , For 12n to end with 0, it should have 2 as well as 5 in its Prime factors to end with 0, Also to end with 5 , it requires at least a single multiple of 5 in its Prime Factors, So 12n cannot end with the digit 0 or 5.
