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kiruha [24]
3 years ago
9

What is –3 2/3 · (–2 1/4 )?

Mathematics
1 answer:
algol [13]3 years ago
6 0
-3\frac{2}{3}\cdot\left(-2\frac{1}4{}\right)=\\--------------------\\negative\ number\ multiply\ by\ negative\ number\ is\ a\ positive\ number\\--------------------\\-3\frac{2}{3}\cdot\left(-2\frac{1}4{}\right)=3\frac{2}{3}\cdot2\frac{1}{4}=\\------------------------------\\

if you want to multiply mixed numbers you need to turn them into improper fractions

3\frac{2}{3}\cdot2\frac{1}{4}=\frac{3\cdot3+2}{3}\cdot\frac{2\cdot4+1}{4}=\frac{9+2}{3}\cdot\frac{8+1}{4}=\frac{11}{3}\cdot\frac{9}{4}=\frac{11}{1}\cdot\frac{3}{4}=\frac{11\cdot3}{1\cdot4}\\\center\boxed{=\frac{33}{4}=8\frac{1}{4}}

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7) PG & E have 12 linemen working Tuesdays in Placer County. They work in groups of 8. How many
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Part A

Since order matters, we use the nPr permutation formula

We use n = 12 and r = 8

_{n}P_{r} = \frac{n!}{(n-r)!}\\\\_{12}P_{8} = \frac{12!}{(12-8)!}\\\\_{12}P_{8} = \frac{12!}{4!}\\\\_{12}P_{8} = \frac{12*11*10*9*8*7*6*5*4*3*2*1}{4*3*2*1}\\\\_{12}P_{8} = \frac{479,001,600}{24}\\\\_{12}P_{8} = 19,958,400\\\\

There are a little under 20 million different permutations.

<h3>Answer: 19,958,400</h3>

Side note: your teacher may not want you to type in the commas

============================================================

Part B

In this case, order doesn't matter. We could use the nCr combination formula like so.

_{n}C_{r} = \frac{n!}{r!(n-r)!}\\\\_{12}C_{8} = \frac{12!}{8!(12-8)!}\\\\_{12}C_{8} = \frac{12!}{4!}\\\\_{12}C_{8} = \frac{12*11*10*9*8!}{8!*4!}\\\\_{12}C_{8} = \frac{12*11*10*9}{4!} \ \text{ ... pair of 8! terms cancel}\\\\_{12}C_{8} = \frac{12*11*10*9}{4*3*2*1}\\\\_{12}C_{8} = \frac{11880}{24}\\\\_{12}C_{8} = 495\\\\

We have a much smaller number compared to last time because order isn't important. Consider a group of 3 people {A,B,C} and this group is identical to {C,B,A}. This idea applies to groups of any number.

-----------------

Another way we can compute the answer is to use the result from part A.

Recall that:

nCr = (nPr)/(r!)

If we know the permutation value, we simply divide by r! to get the combination value. In this case, we divide by r! = 8! = 8*7*6*5*4*3*2*1 = 40,320

So,

_{n}C_{r} = \frac{_{n}P_{r}}{r!}\\\\_{12}C_{8} = \frac{_{12}P_{8}}{8!}\\\\_{12}C_{8} = \frac{19,958,400}{40,320}\\\\_{12}C_{8} = 495\\\\

Not only is this shortcut fairly handy, but it's also interesting to see how the concepts of combinations and permutations connect to one another.

-----------------

<h3>Answer: 495</h3>
5 0
2 years ago
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