First slide

Permutations

Question

If $λ$ is the number of four digit numbers that can be formed by using the digits 1,2,3,4,5,6,7,8 and 9 such that the least digit used is 4,(Repetition of digits is allowed) then the value of $\frac{λ}{3}$ is

Moderate

Solution

$If repetion allowed$
$λ = Required number of numbers$
$\begin{array}{l} = 6^{4} - 5^{4} \\ = 671 \\ ∴ \frac{λ}{3} = \frac{671}{3} = 223.66 \end{array}$

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