There are (n + 1) white and (n + 1) black balls each set numbered 1 to n + 1. The number of ways in which the balls can be arranged in a row so that adjacent balls are of diferent colours, is
A. | (2n+2) ! |
B. | (2n+2) ! x 2 |
C. | (n+1) ! x 2 |
D. | 2[(n+1) ! ]^{2} |
Option: D Explanation : |
Number n of license plates that can be made where each plate contains two distinct letters followed
A. | 486000 |
B. | 468000 |
C. | 498000 |
D. | 489000 |
Option: B Explanation :
n = 26 x 25 x 10 x 9 x 8=468000. |
Suppose a licence plate contains two letters followed by three digits with the first digit not zero. How many different licence plates can be pinted?
A. | 608000 |
B. | 608200 |
C. | 608400 |
D. | 608600 |
Option: C Explanation : Each letter can be printed in twenty-six diferent ways, the first digit in nine ways and each of the other two digits in ten ways. Hence 26 x 26 x 9 x 10 x 10 = 608400 different plates can be printed. |