cam hits the bullseye in 8 darts out of 15 throws. what is the experimental probability that came next throws will hit the bullseye?

A darts player practices throwing a dart at the bull’s eye on a dart board. Her probability of hitting the bull’s eye for each throw is 0.2.

(a) Find the probability that she is successful for the first time on the third throw:

The number F of unsuccessful throws till the first bull’s eye follows a geometric

distribution with probability of success q = 0.2 and probability of failure p = 0.8.

If the first bull’s eye is on the third throw, there must be two failures:

P(F = 2) = p

2

q = (0.8)2

(0.2) = 0.128.

(b) Find the probability that she will have at least three failures before her first

success.

We want the probability of F ≥ 3. This can be found in two ways:

P(F ≥ 3) = P(F = 3) + P(F = 4) + P(F = 5) + P(F = 6) + . . .

= p

3

q + p

4

q + p

5

q + p

6

q + . . . (geometric series with ratio p)

=

p

3

q

1 − p

=

(0.8)3

(0.2)

1 − 0.8

= (0.8)3 = 0.512.

Alternatively,

P(F ≥ 3) = 1 − (P(F = 0) + P(F = 1) + P(F = 2))

= 1 − (q + pq + p

2

q)

= 1 − (0.2)(1 + 0.8 + (0.8)2

)

= 1 − 0.488 = 0.512.

(c) How many throws on average will fail before she hits bull’s eye?

Since p = 0.8 and q = 0.2, the expected number of failures before the first success

is

E[F] = p

q

=

0.8

0.2

= 4.

simplifying

5(x + -6) = 2(x + 3)

reorder the terms:

5(-6 + x) = 2(x + 3)

(-6 * 5 + x * 5) = 2(x + 3)

(-30 + 5x) = 2(x + 3)

reorder the terms:

-30 + 5x = 2(3 + x)

-30 + 5x = (3 * 2 + x * 2)

-30 + 5x = (6 + 2x)

solving

-30 + 5x = 6 + 2x

solving for variable 'x'.

move all terms containing x to the left, all other terms to the right.

add '-2x' to each side of the equation.

-30 + 5x + -2x = 6 + 2x + -2x

combine like terms: 5x + -2x = 3x

-30 + 3x = 6 + 2x + -2x

combine like terms: 2x + -2x = 0

-30 + 3x = 6 + 0

-30 + 3x = 6

add '30' to each side of the equation.

-30 + 30 + 3x = 6 + 30

combine like terms: -30 + 30 = 0

0 + 3x = 6 + 30

3x = 6 + 30

combine like terms: 6 + 30 = 36

3x = 36

divide each side by '3'.

x = 12

simplifying

x = 12

this should .

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