Top 50 सवाल|Half yearly special

In the half yearly exam only 70% if the students were passed. Out of these (passed in half yearly) only 60% student are passed in annual exam. Out of those who did not pass the half yearly exam, 80% passed in annual exam. What per cent of the students passed the annual exam ?

For calculation of interest compounded half yearly, keeping the principal same, which one of the following is true.

in how many years a sum of money trebles at 5% pa.compound interest payable on half yearly basis?