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3 years ago

I need help with 7-12

Mathematics

1 answer:

Anton [14]3 years ago

8 0

7). C

8). 60
n = 5(10) + 10
n = 50 + 10
n = 60

9). 17
f(x) = -2x + 7 plug the -5 in for x
f(x) = -2(-5) + 7
= 10 + 7
= 17

10).
$28.50j < 100 > 18.50s$

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Solve for X<br> 3. 4x - 4<8 AND 9x + 5 > 23

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Answer:

$x \: < \: 3\: and \: x\: > \: 2$

Step-by-step explanation:

The given inequality is

$4x - 4 \: < \: 8 \: and \: 9x + 5 \: > \: 23$

Add 4 to both sides of the first inequality and subtract 5 from both sides of the second inequality.

$4x \: < \: 8 + 4 \: and \: 9x\: > \: 23 - 5$

We simplify to get:

$4x \: < \: 12 \: and \: 9x\: > \: 18$

Divide through the first inequality by 4 and the second by 9.

$x \: < \: 3\: and \: x\: > \: 2$

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3 years ago

Divide 1/5 by 1/2. Input your answer as a reduced fraction.

ad-work [718]

Answer:

2/5

Step-by-step explanation:

1/5 / 1/2= 1/5 x 2/1

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3 years ago

Read 2 more answers

An urn contains n white balls andm black balls. (m and n are both positive numbers.) (a) If two balls are drawn without replacem

Genrish500 [490]

DISCLAIMER: Please let me rename b and w the number of black and white balls, for the sake of readability. You can switch the variable names at any time and the ideas won't change a bit!

Case 1: both balls are white.

At the beginning we have $b+w$ balls. We want to pick a white one, so we have a probability of $\frac{w}{b+w}$ of picking a white one.

If this happens, we're left with $w-1$ white balls and still $b$ black balls, for a total of $b+w-1$ balls. So, now, the probability of picking a white ball is

$\dfrac{w-1}{b+w-1}$

The probability of the two events happening one after the other is the product of the probabilities, so you pick two whites with probability

$\dfrac{w}{b+w}\cdot \dfrac{w-1}{b+w-1}=\dfrac{w(w-1)}{(b+w)(b+w-1)}$

Case 2: both balls are black

The exact same logic leads to a probability of

$\dfrac{b}{b+w}\cdot \dfrac{b-1}{b+w-1}=\dfrac{b(b-1)}{(b+w)(b+w-1)}$

These two events are mutually exclusive (we either pick two whites or two blacks!), so the total probability of picking two balls of the same colour is

$\dfrac{w(w-1)}{(b+w)(b+w-1)}+\dfrac{b(b-1)}{(b+w)(b+w-1)}=\dfrac{w(w-1)+b(b-1)}{(b+w)(b+w-1)}$

Case 1: both balls are white.

In this case, nothing changes between the two picks. So, you have a probability of $\frac{w}{b+w}$ of picking a white ball with the first pick, and the same probability of picking a white ball with the second pick. Similarly, you have a probability $\frac{b}{b+w}$ of picking a black ball with both picks.

This leads to an overall probability of

$\left(\dfrac{w}{b+w}\right)^2+\left(\dfrac{b}{b+w}\right)^2 = \dfrac{w^2+b^2}{(b+w)^2}$

Of picking two balls of the same colour.

We want to prove that

$\dfrac{w^2+b^2}{(b+w)^2}\geq \dfrac{w(w-1)+b(b-1)}{(b+w)(b+w-1)}$

Expading all squares and products, this translates to

$\dfrac{w^2+b^2}{b^2+2bw+w^2}\geq \dfrac{w^2+b^2-b-w}{b^2+2bw+w^2-b-w}$

As you can see, this inequality comes in the form

$\dfrac{x}{y}\geq \dfrac{x-k}{y-k}$

With x and y greater than k. This inequality is true whenever the numerator is smaller than the denominator:

$\dfrac{x}{y}\geq \dfrac{x-k}{y-k} \iff xy-kx \geq xy-ky \iff -kx\geq -ky \iff x\leq y$

And this is our case, because in our case we have

$x=b^2+w^2$
$y=b^2+w^2+2bw$ so, y has an extra piece and it is larger
$k=b+w$ which ensures that k<x (and thus k<y), because b and w are integers, and so b<b^2 and w<w^2