2/5 ÷ x = 4/5
multiply both sides by x to get it out of the denominator.
2/5 = 4/5x
now divide each side by 4/5 to get x by itself.
2/5 ÷ 4/5 = x
divide fractions by multiplying the reciprocal of the divisor.
2/5x × 5/4 = x
10/20 = x
1/2 = x
So 2/5 divided by 1/2 =4/5