Numbers Questions

What is the sum of the first 12 terms of an arithmetic progression if the first term is -19 and last term is 36?

Which of the following can't be the unit's digit of a perfect square?

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

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

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

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.

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)?