A boy spends 3/4 of his pocket money and then 4/5 of the remainder is given to is sister . if he has rupees 40 left ,what did he have first 

a boy spends 3/4 of his pocket money , that means 1/4 is left

4/5 of the remainder is given to sister

he has Rs40 left

total money as remainder=5/5

money left from remainder after giving to sister=5/5-4/5=1/5

1/5=Rs 40

then , 5/5=40 x 5 =Rs 200

therefore total money as remainder before givinf to sister = Rs 200

3/4 of pocket money spent , then left is 1/4

as we know remainder money was Rs 200 so 1/4 =Rs200

then 3/4 = 200 x 3 =Rs600

total money at the begining or total pocket money before spending=money spent  + money left

  Rs600+Rs200= Rs 800

therefore the boy had Rs 800 at first