Permutation Combination Question 16
Question 16 - 31 January - Shift 1
Let 5 digit numbers be constructed using the digits $0,2,3,4,7,9$ with repetition allowed, and are arranged in ascending order with serial numbers. Then the serial number of the number 42923 is
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Answer: 2997
Solution:
Formula: Non-Consecutive Selection
$2++++=1296$
$\begin{matrix} 6 & 6 & 6 & 6\end{matrix} $
$3++++=1296$
6666
$40+++=216$
666
$420++=36$
66
$\underline{4} \underline{2} \underline{2}++=36$
$423++=36$
66
$424++=36$
66
$427++=36$ 66
$4290+=6$
6
$42920=1$
$42922=1$
$42923=1$
$=2997$
