设甲数为x,乙数为y
/x-y/=2/5
x-y=2/5orx-y=-2/5
3/4x=5/6y
9x=10y
x:y=10:9
x=10k,y=9k
x-y=k=2/5
x=4,y=18/5,or
x-y=k=-2/5
x=-4,y=-18/5
x+y=4+18/5=38/5
orx+y=-4-18/5=-(4+18/5)=-38/5
甲,乙两数的和是38/5or-38/5