Find the value of $$ {1\over{2×5}}+{1\over {5×8}}+{1\over {8 × 11}}+......{1\over {23 × 26}}=?$$

Find the average of all prime numbers from 1 to 20?

If the arithmetic means of 3a and 4b is greater than 50, and a is twice b, then the smallest possible integer value of a is: 

How many numbers can be completely divided to 240?

What least value which should be added to 1812 to make it divisible 7,11 and 14? 

What is the largest four digit number which is also complete?

If an 8-digit number 1862383A is divisible by 22, find the value of A.

The greatest number less than 1500, which is divisible by both 16 and 18, is: