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Question

Mathematics Question on Permutations

How many different nine digit numbers can be formed from the number 223355888223355888 by rearranging its digits so that the odd digits occupy even positions?

A

16

B

36

C

60

D

180

Answer

60

Explanation

Solution

XXXXXX - X - X - X - X
The four digits 3,3,5,53,3,5,5 can be arranged at ()(-) places in 4!2!2!=6\frac{4 !}{2 ! 2 !}=6 ways.
The five digits 2,2,8,8,82,2,8,8,8 can be arranged at (X)( X ) place in 5!2!3!=10\frac{5 !}{2 ! 3 !}=10 ways.
Total number of arrangements is 6×10=606 \times 10=60.