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posledela
4 years ago
13

Jan is saving for a skateboard. She has saved $30 already, which is 20% of the total price. How much does the skateboard cost

Mathematics
1 answer:
White raven [17]4 years ago
4 0
She has $30=20% of the total price so basically add 80% to 30. The total amount the skateboard costs is $150.00 she still needs $120.00 more
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Show that if X is a geometric random variable with parameter p, then
Lubov Fominskaja [6]

Answer:

\sum_{k=1}^{\infty} \frac{p(1-p)^{k-1}}{k}=-\frac{p ln p}{1-p}

Step-by-step explanation:

The geometric distribution represents "the number of failures before you get a success in a series of Bernoulli trials. This discrete probability distribution is represented by the probability density function:"

P(X=x)=(1-p)^{x-1} p

Let X the random variable that measures the number os trials until the first success, we know that X follows this distribution:

X\sim Geo (1-p)

In order to find the expected value E(1/X) we need to find this sum:

E(X)=\sum_{k=1}^{\infty} \frac{p(1-p)^{k-1}}{k}

Lets consider the following series:

\sum_{k=1}^{\infty} b^{k-1}

And let's assume that this series is a power series with b a number between (0,1). If we apply integration of this series we have this:

\int_{0}^b \sum_{k=1}^{\infty} r^{k-1}=\sum_{k=1}^{\infty} \int_{0}^b r^{k-1} dt=\sum_{k=1}^{\infty} \frac{b^k}{k}   (a)

On the last step we assume that 0\leq r\leq b and \sum_{k=1}^{\infty} r^{k-1}=\frac{1}{1-r}, then the integral on the left part of equation (a) would be 1. And we have:

\int_{0}^b \frac{1}{1-r}dr=-ln(1-b)

And for the next step we have:

\sum_{k=1}^{\infty} \frac{b^{k-1}}{k}=\frac{1}{b}\sum_{k=1}^{\infty}\frac{b^k}{k}=-\frac{ln(1-b)}{b}

And with this we have the requiered proof.

And since b=1-p we have that:

\sum_{k=1}^{\infty} \frac{p(1-p)^{k-1}}{k}=-\frac{p ln p}{1-p}

4 0
4 years ago
PLEASE HELP!!! ILL GIVE BRAINLIEST !! Which is the correct answer ? 100 POINTS !! EXPLAIN.
murzikaleks [220]

Answer:

the correct answer would be B

3 0
3 years ago
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The center of a circle is (4, 6), and an endpoint of a diameter is (2, 5). What is the other endpoint of the diameter?
valentinak56 [21]
Consider this option:
1. if the point (4;6) is the centre of the circle and the point (2;5) is the first endpoint of its diameter, then point (4;6) is the middle point of the diameter (it means that is the middle between the 1st and the 2d endpoints of diameter).
2. using the property described above:
for x of the 2d endpoint of the diameter: x=4*2-2=6;
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answer: (6;7)
3 0
3 years ago
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A number increased by 100% and decreased by 20% is x. what is the number ? NEEDED TODAY
vodka [1.7K]

Answer:

Let's assume the number be 100.

According to the problem , 100 is increased by 100%.

So, new number will be 100+100=200

Now 200 will decreased by 20%.

So, 20% of 200= 0.20*200= 40.

So, again the number has been changed into 200+40=240.

So, x=240

Step-by-step explanation:

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3 years ago
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seraphim [82]

Answer:

9

Step-by-step explanation:

divied by 3

27  divided by 3 is 9

plz mark brainliest

4 0
3 years ago
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