Сколько будет: b-a/5 : a/5 - ab-b/ab
1) ( b - a )/5 : ( a/5 ) = ( b - a )/a 2) ( ab - b )/ab = ( b( a - 1 ))/ab = ( a - 1 )/a 3) ( b - a )/a : ( a - 1 )/a = ( b - a )/( a - 1 )