What value will come in place of question mark (?) in the questions given below?

663.48 + 22.51 - 292.63 = ? + 300.44 

Find the sum of 30²+31²+32²+________+80²

Sum of two numbers is 15 and sum of their reciprocals is $$ {15\over56}$$. The two numbers are

If two numbers are each divided by the same divisor, the remainders are respectively 3 and 4. If the sum of the two numbers be divided by the same divisor, the remainder is 2. The divisor is 

The least number that must be subtracted from 1294 so that the remaining number when divided by 9, 11, 13 will leave in each case the same remainder 6 is:

What value will come in place of question mark (?) in the questions given below?

837 ÷ ? × 0.8 = 9.3 

Three numbers are such that if the average of any two of them is added to the third number, the sums obtained are 168, 174 and 180 respectively. What is the average of the original three numbers?

The mean of 20 items is 55. If two items 45 and 30 are removed, what will be the new mean of the remaining items?