15/56
15--------> we can obtain it by multiplying 3x5,5x3,1x15,15x1
56--------> we can obtain it by multiplying 8x7,4x14,2x28,7x8
a=3/8 b=5/7---------->
a*b=(3*5)/(8*7)=15/56
a=5/4 b=3/14---------> a*b=(5*3)/(4*14)=15/56
a=1/2 b=15/28--------> a*b=(1*15)/(28*2)=15/56
