a)x= 40/100 *y= 10/25 *y= 2/5*y
x= 2y/5
x/y= 2y/5/y= 2y/5 * 1/y= 2/5
b)(3x+y)/(x+y)= (3*2y/5 +y)/(2y/5 +y)=
=(6y/5 +y)/ (2y/5 +y)=
= (6y+5y)/5 / (2y+5y)/5=
= 11y/5 /7y/5=
= 11y/5 * 5/7y= 11/7
c)p% din x=y
p/100 * 2y/5=y
p/50 * y/5=y
p/50= y/y/5
p/50= y * 5/y
p/50=5
p=5*50=250%