12 kg of rice costing 30 per kg is mixed with 8 kg of rice costing 40 per kg. The average per kg price of mixed rice is

There are 10 balls, some of them are red and the others white. The average cost of all the balls is Rs. 28, average cost of red balls Rs. 25 and that of white balls is Rs. 30, the number of white balls is: 

The mean of 9 observations is 16. One more observation is included and the new mean becomes 17. The 10th observation is

The average age of five girls is 11. The oldest among them is 15 years old. What is the average age of the others?

The average score in Mathematics of 90 students of section A and B of class IX was 63. The number of students in A were 10 more than those in B. The average score of students in A was 30% more than that of students in B. The average score of students in B is:

The average of three numbers a, b and c is 2 more than c. The average of a and b is 48. If d is 10 less than c, then the average of c and d is:

What is the average of the first five prime numbers?

The average age of six members of a family is 40 years. If the age of a guest is included, then the average age increases by 12.5%. What is the age (in years) of the guest?