Numbers Questions

What will come in the place of the question mark (?) in the following number series?305, 338, 404, 503, 635 , (?)

Which of the following numbers is not a prime number?

By what least number should 1200 be multiplied so that it becomes a perfect square?

Find the average of all prime numbers between 20 and 50.

What is the sum of all prime numbers between 60 and 80?

ΔABC is right angled at B. BD is an altitude. DC = 9 cm and AC = 25 cm. What is the value of BC (in cm)?

If the 1st and the 3rd term of an arithmetic progression are -10 and -4, what is the 12th term?

Out of a group of three numbers, second is thrice of the first and also twice of the third. If the sum of the three numbers is 55 then find the largest number in the group.