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4 years ago

Need help w this plz:(

Mathematics

1 answer:

steposvetlana [31]4 years ago

8 0

Answer:

cant see i am dumb

Step-by-step explanation:

and blind i cant see at all my gide dog wrote dis woof woof

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A radioactive substance is decaying exponentially. If there are initially 15 grams of the substance and after 3 hours there are

sukhopar [10]

Answer:

Ok, an exponential decay is written as:

P(t) = A*(1 - r)^t

Where A is the initial population, r is the rate of decay and t is the unit of time.

We know that the initial population is 15g

then:

P(t) = 15g*(1 - r)^t

And at t = 3hs, the populations is 5g

P(5h) = 5g = 15g*(1 - r)^5

5/15 = 1/3 = (1 - r)^5

(1/3)^(1/5) = (1 - r) = 0.8

Now, the half life time of the sustance is t = x, such that the population reduces to it's half:

P(x) = A/2 = 15g/2 = 7.5g

Then:

7.5g = 15g*0.8^x

7.5g/15g = 1/2 = 0.8^x

Now, remember that if we have:

a = b^x

then

x = ln(a)/ln(b)

ln(1/2)/ln(0.8) = x = 3,11 hours

3 0

3 years ago

Solve the equation: x^2 - 6x = 7 A. x = 7 , 1 B. x = -7 , 1 C. x = 7 , -1

Alex777 [14]

x^2 - 6x = 7
(x - 7)(x + 1)= 0
x = 7, - 1

The answer is: x = 7, -1.

6 0

4 years ago

You have two parents, four grandparents, eight greatgrandparents, and so forth.

Leviafan [203]

A.
In the first generation we have 2 ancestors.
In the second generation we have 4 ancestors or $2^{2}$ ancestors.
In the third generation we have 8 ancestors ot $2^{3}$ ancestors.

We can see that each succesive generation has two times more members. The sum is:
$2+4+8+16+...+ 2^{40}$

To calculate number of ancestors we can use formula for the sum of a geometric sequence. Geometric sequence is sequence of numbers that differ by a certain factor. This factor is called ratio. Formula is:
 $S= a_{1} * \frac{1- r^{n} }{1-r}$
Where:
S -> sum
a1 -> first member of a sequence
r -> ratio
n -> number of elements

For this question:
a1 = 2
r = 2
n = 40
 $S= 2* \frac{1- 2^{40} }{1-2} =2 199 023 255 550$

b.
1 generation = 25 years
40 generations = 40 * 25 = 1000 years

c.
Total number of people who have ever lived = $10^{10}$
Number of ancestors in 40 generations = $2.2*10^{12}$

The number of ancestors is greater than total number of people who have ever lived. This means that not all ancestors were distinct and that in each generation both men and women had children with more than one partner.

8 0

3 years ago

2 Points

mart [117]

Answer:

B. Doubled

Step-by-step explanation:

The formula to find the circumference of the circle is

$C=2\pi r$