How many ways can you buy 2 DVDs from a

Reese Estes 2022-05-09 Answered
How many ways can you buy 2 DVDs from a display of 15?
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Answers (2)

verrainellewtzri
Answered 2022-05-10 Author has 13 answers
Step 1
We assume that someone will not buy two of the same DVD.
For the first DVD, there is a choice of 15 , but once the first is bought, there is a choice of 14 for the second one.
There are 15 × 14 choices = 210.
Step 2
However, this does not take order into consideration .... the 2 DVD's might be the same, just bought in a different order, so we need to divide this number by 2 to avoid the duplicates.
210 2 = 105
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Jaime Coleman
Answered 2022-05-11 Author has 3 answers
Step 1
Assumption: choosing a + b is classified the same as choosing b + a .
This is the condition of 'combinations'
Step 2
. n C r n ! ( n - r ) ! r !
. n C r . 15 C 2 15 ! ( 15 - 2 ) ! 2 !
= 15 × 14 × 13 ! 13 ! . 2 ! = 15 × 14 2
= 105
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