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xenn [34]
3 years ago
14

A bag contains 8 black beads and 4 white beads. If 2 beads are drawn at random, what is the probability that both beads are blac

k?
Mathematics
1 answer:
maria [59]3 years ago
3 0

Answer:

14/33

Step-by-step explanation:

The total amount of beads is 8+4 = 12.  8 of these are black beads, so that is what we want, so 8/12 or 2/3.  For the second one, one black bead is already taken so 8-1 = 7 are left and for the total 12 - 1 = 11 are left, so 7/11.  Multiply this by 2/3 and we get 14/33.

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Nikolay [14]

Replace x with π/2 - x to get the equivalent integral

\displaystyle \int_{-\frac\pi2}^{\frac\pi2} \cos(\cot(x) - \tan(x)) \, dx

but the integrand is even, so this is really just

\displaystyle 2 \int_0^{\frac\pi2} \cos(\cot(x) - \tan(x)) \, dx

Substitute x = 1/2 arccot(u/2), which transforms the integral to

\displaystyle 2 \int_{-\infty}^\infty \frac{\cos(u)}{u^2+4} \, du

There are lots of ways to compute this. What I did was to consider the complex contour integral

\displaystyle \int_\gamma \frac{e^{iz}}{z^2+4} \, dz

where γ is a semicircle in the complex plane with its diameter joining (-R, 0) and (R, 0) on the real axis. A bound for the integral over the arc of the circle is estimated to be

\displaystyle \left|\int_{z=Re^{i0}}^{z=Re^{i\pi}} f(z) \, dz\right| \le \frac{\pi R}{|R^2-4|}

which vanishes as R goes to ∞. Then by the residue theorem, we have in the limit

\displaystyle \int_{-\infty}^\infty \frac{\cos(x)}{x^2+4} \, dx = 2\pi i {} \mathrm{Res}\left(\frac{e^{iz}}{z^2+4},z=2i\right) = \frac\pi{2e^2}

and it follows that

\displaystyle \int_0^\pi \cos(\cot(x)-\tan(x)) \, dx = \boxed{\frac\pi{e^2}}

7 0
1 year ago
If x = 2 and y = -3, what is the value of 2x^2 + 3xy – 2y^2?
sammy [17]

Answer: Given as,X=2 & Y=3,

now multiplying we get,

2xxy=2×2×3=12

Ans.) 12

Step-by-step explanation:

7 0
2 years ago
The area of the shape is 54 cm2.<br> Find the value of r.
Bond [772]
Radius is half the circumference
c= 2(square root) pieA
4 0
2 years ago
Gilyann got a new puppy for her birthday. She went to the pet store to buy what she needed for the puppy: a food dish for $7.95,
Elina [12.6K]

Answer:

76.48

Step-by-step explanation:

5 0
2 years ago
Which is another way to check the sum of 104+34+228+877?
Alex787 [66]
The answer is digit sum method.

Digit sum method is method used to check the sum of sum numbers. If the sum of all of the digits of numbers is equal to the sum of all of the digits of the total sum, then the arithmetic process was correct.

We need to check the sum of <span>104+34+228+877:
</span>104 + 34 + 228 + 877 = 1243

Let's first summarize the digits of individual numbers:
104 *** 1 + 0 + 4 = 5
34 *** 3 + 4 = 7
228 *** 2 + 2 + 8 = 12 *** 1 + 2 = 3
877 *** 8 + 7 + 7 = 22 *** 2 + 2 = 4

Now, let's sum these sums:
5 + 7 + 3 + 4 = 19 *** 1 + 9 = 10 *** 1 + 0 = <u><em>1</em></u>

Then, let's summarize the digits of the total sum:
1243 *** 1 + 2 + 4 + 3 = 10 *** 1 + 0 = <u><em>1</em></u>

Since the sums of the digits on the both sides of equation is 1, than the arithmetic process was correct and the sum of <span>104 + 34 + 228 + 877 is really 1243.</span>

7 0
3 years ago
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