From 1,2,3,4,5,6,7 how many 6 digit number combinations can u find without reputation and 2nd last digit must be even
Asked in/Preparing for : tcs


1 Respond


There are two approaches for this problem

 

APPROACH#1
2nd last digit can be selected from any `3` no. `(2, 4, 6)` = 3C1 ways

Places left `= 5` digits left `= 6`
so first select(combination) any 5 digit from the 6 and then arrange(permutation) them for those 5 places
`=` 6C5 `xx 5! ` `(` in `5!` ways those `5` numbers can be places in blank `5` places`)`
 
3C1 `xx`  6C5 `xx 5! = 2160`
 
APPROACH#2
2nd last digit can be selected from any `3` no. `(2, 4, 6)` `=` 3C1 ways
select `1` number from remaining `6` for place no. `1`
select `1` number from remaining `5` for place no. `2`
select `1` number from remaining `4` for place no. `3`
select `1` number from remaining `3` for place no. `4`
select `1` number from remaining `2` for place no. `6`
3C1 `xx` 6C1 `xx` 5C1 `xx` 4C1 `xx` 3C1 `xx` 2C1 `= 2160`

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