How many 10 digits numbers can be written by using the digits 1 and 2 ?
A. | ^{10}C_{1} + ^{9}C_{2} |
B. | 2^{10} |
C. | ^{10}C_{2} |
D. | 10! |
Option: B Explanation : |
In an examination there are three multiple choice questions and each question has 4 choices. Number of ways in which a student can fail to get all answers correct is
A. | 11 |
B. | 12 |
C. | 27 |
D. | 63 |
Option: D Explanation : |
The number n of ways that an organization consisting of twenty -six members can elect a president, treasurer, and secretary (assuming no person is elected to more than one position) is
A. | 15600 |
B. | 15400 |
C. | 15200 |
D. | 15000 |
Option: A Explanation :
The president can be elected in twenty-six different ways; following this, the treasurer can be elected in twenty five different ways since the person chosen president is not elegible to be treasurer); and following this, the secretary can be elected in twenty-four different ways. Thus, by above principle of counting, there are |
Ten different letters of an alphabet are given. Words with five letters are formed from these given letters. Then the number of words which have at least one letter repeated is
A. | 69760 |
B. | 30240 |
C. | 99748 |
D. | none of these |
Option: A Explanation : |