Question

Does my solution make sense?

You're required to select 4 different numbers from 1 -25 so that the sum of the 4 numbers is odd.

My solution:
Number of odd nos = 13
Number of even nos =12

Case 1, 1 even no and 3 odd numbers are selected
No. of selection = 13C3 x 12C1 = 3432

Case 2, 1odd no and 3 even nos are selected
no. of selection = 13C1 x 12C3 = 2860

Total number of selection = 3432 +2860 = 6292

Answer 1

must be right ..

Answer 2

Actually, this is a mc question with the following choices
A. 2860
B. 3432
C. 6292
D. 7436

Answer 3

there's an answer there

Answer 4

Another problem is that I'm not sure why I used C instead of P even though I can work out the 'answer'

Answer 5

Looks good to me

Answer 6

order does not matter 1 2 4 6 is the same as 2 4 6 1, etc

Answer 7

it's just a selection ... not in order

Answer 8

How do i know if order is important? (since 'order' is the only to differentiate C and P)

Answer 9

*only way

Answer 10

You're required to select 4 different numbers

if you select 1 2 4 6 is the same or different from 2 4 6 1 ?

Answer 11

In other words, make your selection in any order you want, put them in a hat. The order you selected them in is lost once you put them in the hat.

Answer 12

there is difference when you say "select 4 boys from 10 for this group" and when you say " arrange four boys in first bench out of 10"

Answer 13

So, in this case,order is not important, while when the question is like, 3numbers are selected to make a 3-digit number, then the order is important, and we should use P instead of C?

Answer 14

yes

Answer 15

Okay, I think I got it. Thanks everyone :)