
Vinay D. answered 03/30/16
Tutor
4.8
(12)
Software Engineer with over 13 years of experience in programming.
It has been a long time since I tried permutations and combinations but let me give a shot
See, you have 13 cards available and you want to draw 3 cards but the sum should be 22. Now, lets first see how many unique options give 22 as sum
1. 10 10 2
2. 10 9 3
3. 10 8 4
4. 10 7 5
6. 10 6 6
There are 6 unique combinations. But the list is unordered which means any number can come anywhere between q to 3 draws. Therefore, use permutation formula here. You have 3 spots available and how many number can fill each spot.
1. 10 10 2 gives 3 different ways
That is 10 10 2, 10 2 10, 2 10 10
2. 10 9 3 gives 6 different ways
That is 10 9 3, 10 3 9, 3 10 9, 3 9 10, 9 3 10, 9 10 3
Similarly
3. 10 8 4 gives 6 different ways
4. 10 7 5 gives 6 different ways
5. 10 6 6 gives 3 different ways
Ans should be 24.