When you have to divide a fraction, you have to invert the second fraction (4/7 becomes 7/4), and you then multiply the two fractions.
=2/5 ÷ 4/7
=2/5 * 7/4
Multiply the numerators on top
Multiply the denominators on bottom
=(2*7)/(5*4)
=14/20
Simplify by dividing 2 into top & bottom
=7/10
Hope this helps!! :)