A student taking an examination is required to answer exactly 10 out of 15 questions.
I think i'm supposed to use combination right? Order does not matter? Because it can be any choice of the 10 questions? I am usually horrible deciphering what to do but I think with permutation I must look out for the keywords "arrange" or "order".
What is your question?
I just want to know if I should use the combination formula.
Yes, you are correct. In this case, you need to use combinations, not permutations. Combinations are used when the order of selection does not matter, while permutations are used when the order of selection does matter.
Since the order of answering the questions doesn't matter, you should use combinations to find the number of ways the student can select 10 questions out of the 15 available.
To solve this, you can use the formula for combinations, which is:
nCr = n! / (r! * (n - r)!)
Where:
- n is the total number of items (in this case, the total number of questions, which is 15).
- r is the number of items you want to choose (in this case, the number of questions the student needs to answer, which is 10).
- ! represents the factorial of a number (for example, 5! is equal to 5 x 4 x 3 x 2 x 1).
So, using the combination formula, you can calculate the number of ways the student can select 10 questions out of 15.