The given diagram shows the number of students who failed in an examination comprising papers of English, Hindi and Mathematics. The total number of students who took the test is 500. What is the percentage of students who failed in at least two subjects? 
A sum of Rs. 800 amounts to Rs. 920 in 3 years at simple interest. What would be the amount, if the interest rate is increased by 3%?
In what ratio must water be mixed with milk to gain 20% by selling the mixture at cost price?