Sequences and S...

Total number of ways of selecting two numbers from the set $${1,2,3,...90}$$ so that their sum is divisible by $$3$$ is

The number of $$n$$ digit numbers which consists of the digits $$1$$ & $$2$$ only if each digits is to be used atleast once, is equal to $$510$$  then $$n$$ is equal to

Fill in the missing values.

Find the missing number, if same rule is followed in all the three figures.

The value of $$\displaystyle\sum^{10}_{r=0}(r)$$ $$^{20}C_r$$ is equal to?

Find the missing number in the given figure?

A student is to answer 10 out of 13 questions in an examination such that he must choose at least 4 from the first five questions. The number of choices available to him is 

If $$\displaystyle\sum^m_{k=1}(k^2+1)k!=1999(2000!)$$, then m is?

If $$24 + 37 = 7,12 + 18 = 3$$, then 54+21=?

In the following number series,one number is wrong.find out the ?

1,2,8,33,149,765,4626