Question

Write the number of 5 digit numbers that can be formed using digits 0, 1 and 2.

Answer 1

Number of ways in which the first digit can be filled = Number of digits available for filling it = 2 {1,2} (Since the first one cannot be 0)
Number of ways of filling the remaining four palaces = 3 each (as each place can be filled with either 1, 2 or 0)
By fundamental principle of counting, number of five digit numbers that can be formed = 2$\times$3$\times$3$\times$3$\times$3 = 2$\times$3⁴