4/5x=3/10
x = 3/10 ÷ 4/5 = 3/10×5/4 = 3/8
x÷6/7=1/7
x = 1/7×6/7 = 6/49
x× 2/5 = 4
x = 4÷2/5 = 4 ×5/2 = 10
3/4+x=7/8
x = 7/8 - 3/4 = 7/8 - 6/8 = 1/8
x-1/2=4/5
x = 4/5 + 1/2 = 8/10 + 5/10 = 13/10 = 1 3/10(1又3/10)
3x = 25
x = 25/3 = 8 1/3(8又1/3)