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# In a box of 10 electrical parts, 2 are defective. (a) If you

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In a box of 10 electrical parts, 2 are defective. (a) If you [#permalink]  30 May 2019, 16:21
Expert's post
In a box of 10 electrical parts, 2 are defective.

(a) If you choose one part at random from the box, what is the probability that it is not defective?
(b) If you choose two parts at random from the box, without replacement, what is the probability that both are defective?

[Reveal] Spoiler: OA
(a) $$\frac{4}{5}$$ (b) $$\frac{1}{45}$$

Math Review
Question: 12
Page: 297
Difficulty: medium

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Re: In a box of 10 electrical parts, 2 are defective. (a) If you [#permalink]  31 May 2019, 08:06
Expert's post
Carcass wrote:
In a box of 10 electrical parts, 2 are defective.

(a) If you choose one part at random from the box, what is the probability that it is not defective?
(b) If you choose two parts at random from the box, without replacement, what is the probability that both are defective?

[Reveal] Spoiler: OA
$$(a) \frac{4}{5} (b) [m]1/45$$[/m]

Math Review
Question: 12
Page: 297
Difficulty: medium

(a) If you choose one part at random from the box, what is the probability that it is not defective?
Among the 10 parts, 2 are defective and 8 are not defective
S, P(select a non-defective part = 8/10 = 4/5

-------------------------------------
(b) If you choose two parts at random from the box, without replacement, what is the probability that both are defective?
P(BOTH parts are defective) = P(1st part is defective AND 2nd part is defective)
= P(1st part is defective) x P(2nd part is defective)
= 2/10 x 1/9
= 2/90
= 1/45

Cheers,
Brent
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Brent Hanneson – Creator of greenlighttestprep.com
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Re: In a box of 10 electrical parts, 2 are defective. (a) If you   [#permalink] 31 May 2019, 08:06
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