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3 years ago

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Mathematics

1 answer:

WINSTONCH [101]3 years ago

3 0

Answer:

Step-by-step explanation:

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-7.4 + 4.45 =<br> A 11.85<br> B 2.95<br> C -2.95<br> D -11.85

const2013 [10]

-7.4 + 4.45 = -2.95 so C

5 0

3 years ago

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Dewey's soccer team purchased uniforms and equipments for a total cost of $912 . The equipment cost $ 612 , and the uniforms cos

love history [14]

Answer:

12 uniforms

Step-by-step explanation:

first you subtract 612 from 912 and get 300

then you divide 300 by the cost of uniforms (25)

then you get an answer of 12

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3 years ago

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Suppose an unknown radioactive substance produces 8000 counts per minute on a Geiger counter at a certain time, and only 500 cou

mariarad [96]

Answer:

The half-life of the radioactive substance is of 3.25 days.

Step-by-step explanation:

The amount of radioactive substance is proportional to the number of counts per minute:

This means that the amount is given by the following differential equation:

$\frac{dQ}{dt} = -kQ$

In which k is the decay rate.

The solution is:

$Q(t) = Q(0)e^{-kt}$

In which Q(0) is the initial amount:

8000 counts per minute on a Geiger counter at a certain time

This means that $Q(0) = 8000$

500 counts per minute 13 days later.

This means that $Q(13) = 500$ . We use this to find k.

$Q(t) = Q(0)e^{-kt}$

$500 = 8000e^{-13k}$

$e^{-13k} = \frac{500}{8000}$

$\ln{e^{-13k}} = \ln{\frac{500}{8000}}$

$-13k = \ln{\frac{500}{8000}}$

$k = -\frac{\ln{\frac{500}{8000}}}{13}$

$k = 0.2133$

$Q(t) = Q(0)e^{-0.2133t}$

Determine the half-life of the radioactive substance.

This is t for which Q(t) = 0.5Q(0). So

$Q(t) = Q(0)e^{-0.2133t}$

$0.5Q(0) = Q(0)e^{-0.2133t}$

$e^{-0.2133t} = 0.5$

$\ln{e^{-0.2133t}} = \ln{0.5}$

$-0.2133t = \ln{0.5}$

$t = -\frac{\ln{0.5}}{0.2133}$

$t = 3.25$

The half-life of the radioactive substance is of 3.25 days.

7 0

3 years ago

Peter wants to use 75-watt lightbulbs and other electronics in his tree house. He has one outlet with a maximum of 900 watts. Wh

ohaa [14]

Expression is 900 - 75n

Step-by-step explanation:

Step 1: Maximum watts that can be used is 900W. Find amount of watts used by n light bulbs.

⇒ Watts used by n light bulbs = 75 × n = 75n

Step 2: To find the remaining amount of wattage, subtract the maximum possible W and the watts used by the light bulbs.

⇒ 900 - 75n

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3 years ago

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In order to buy a $38 pair of shoes, you have to borrow $16 from your friend. How much money did you start with

Aleksandr-060686 [28]

Answer:

22 dollars

Step-by-step explanation:

38 - 16 = 22

if they cost 38 subtract the amount you borrowed(16) and you get what you started with(22)

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3 years ago

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