The average of a list of integers goes up by 2 when 30 is added to the list. If 7 is added to the new list, then the average reduces by 1. How many numbers were there in the original list?

There are 9 yellow balls, 13 pink balls, and 15 purple balls in a bag. What is the probability of picking up one pink ball out of the bag without looking?

The diagonal of following quadrilateral ABCD is 30 cm long, and length of perpendiculars dropped on diagonal are 9 cm and 15 cm. Find the area of quadrilateral.

The graph below shows the temperature (in degrees Celsius) over 10 weeks in Fukuoka and Hiroshima. Find the difference in temperature of two cities in the week when difference is maximum.

{a_{m}} is a sequence of integers such that a_{1} = 1, and and a_{m+n} = a_{m} + a_{n} + mn, for all positive integers m and n. What is the value of a_{15}?