The numbers 1, 2,.., 1 0 are written on the board. A person can pick two numbers, a and b on the board, erase them, and replace them with the number a+b-1. (a) How many times can one repeat this process unti there is just one rumber on the board?

The numbers 1,2,..,10 are written on the board.A person can pick two numbers,a and b on the board,erase them,and replace them with the number a +b-1. (a) How many xx can one repeat this process unti there is just one rumber on the board?

Numbers 1,2, and 3 are written on three cards. How many two digit numbers can be formed by placing two cards side by side?

The integers 1, 2, …., 40 are written on a blackboard. The following operation is then repeated 39 times, In each repetition, any two numbers, say a and b, currently on the blackboard are erased and a new number a+b-1 is written. What will be the number left on the board at the end?

Four balls with the numbers 1,2,3,4 written on them are put in a box. They are drawn one by one (without replacement) at random. In how many ways it can happen that the ordinal number of atleast one ball coincide with its own number ?

Four slip of papers with the number 1,2,3,4 written on them are put in a box. They are drawn one by one (without replacement) at random. In how many ways it can happen that the ordinal number of atleast one slip coincide with its own number?

The number 3 can be written as 3,2+1,1+2 or 1+1+1 in four ways.In how many ways number n can be written as?

How many 4 digits numbers can be formed from the digits 1 to 10 if not digit can be repeated.

The product of two numbers is (-1)/(4) . If one of them is (-3)/(10) , then the other is