In an examination, student gets on average 76 marks. The total marks for five subjects is 500. His marks in 4 subjects are mentioned, calculate the marks obtained by the student in Mathematics marked ass 'x' in the below table.
A sum of Rs 10000 becomes Rs 14641 when invested at compound interest at the yearly interest rate of 20% per annum. If the compounding is done half yearly, then for how many years was the sum invested?