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Featured 9 months ago

30,421,755 CDs. Realistic to make a CD of every combination? No. Practical? What is practicality to a true music lover?!?!?!

We have 28 songs and we're going to find how many ways we can put sets of 12 songs onto CDs. Since order doesn't matter (having songs 1 - 12 on a CD is the same as having songs 12 - 1 on the CD), we'll use the Combination calculation, which is:

And now let's evaluate this fraction:

There's a lot of cancelations, so I'll use colours to help keep track:

Let's clean this up and do one more round... I'm going to express 26 as

(To avoid the long and involved calculations, you can use the Combination calculator tool here: http://www.calculatorsoup.com/calculators/discretemathematics/combinations.php)

Featured 7 months ago

Use the identity

Recall the identity

To prove this as

=

#(nxx(n-1)!)/(kxx(k-1)!(n-k)(n-k-1)!)# =

#((n-1)!)/((k-1)!(n-k-1)!)[n/(k(n-k))]# =

#((n-1)!)/((k-1)!(n-k-1)!)[((n-k)+k)/(k(n-k))]# =

#((n-1)!)/((k-1)!(n-k-1)!)[1/k+1/(n-k)]# =

#((n-1)!)/(k(k-1)!(n-k-1)!)+((n-1)!)/(k(k-1)!(n-k)(n-k-1)!)# =

#((n-1)!)/(k!(n-k-1)!)+((n-1)!)/(k!(n-k)!)=((n-1),(k))+((n-1),(k-1))#

Hence

#((n-1),(k-1))=((n-2),(k-1))+((n-2),(k-2))#

Hence

Now similarly split

#((n-2),(k-2))=((n-3),(k-2))+((n-3),(k-3))# and

Going on similarly, we get

Featured 6 months ago

An alternative way to do this is to use equations for combinations, the general formula for which is:

We want our hand to have exactly one Ace. Since there are four aces in a deck, we can set

But we also need to account for the other four cards in our hand. There are 48 cards to pick from, so we can set

We multiply them together to find the total number of ways we can get exactly one Ace in our hand:

~~~~~

To figure out the probability, we also need to know the total number of 5-card hands possible:

Let's evaluate it!

And so:

Featured 3 months ago

From software:

From table lookup:

If we seek an 88% confidence interval, that means we only want a 12% chance that our interval does not contain the true value. Assuming a two-sided test, that means we want a 6% chance attributed to each tail of the

This

Find the closest value in the table to 0.9400 as you can, then see what its row and column is. From observation, we see that 0.9394 and 0.9406 are in the table with

**Note:** We could also get an answer from software like R, by typing the command

Featured 2 weeks ago

Let's find the number of ways all boys will go, then find the number of ways all girls will go, then add them together. Then we'll find the probability.

We're working with combinations (we don't care in what order the kids are picked). That general formula is:

I'll use

**All boys**

From the population of 5 boys, 3 are picked. From the population of girls, none are picked:

**All girls**

From the population of 6 girls, 3 are picked. From the population of boys, none are picked:

**Total ways**

**Probability**

We now have the total number of ways to meet the condition of having 3 of the same sex go on the field trip. How many different ways can we select 11 children to go? There are 11 children in total and we're picking 3:

And so that gives us:

Featured 2 weeks ago

We're adding combinations, where the general formula is:

Let's substitute in values:

ⁿ⁺¹c₅+ⁿ⁺²c₅+ⁿ⁺³c₅+ⁿ⁺⁴c₅

I'm going to simplify each fraction first before trying to combine them. Remember that

Know that

And we can simplify a bit more:

And now to see if I got the math right. Suppose

And from the expression we've found:

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