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In a bulb factory there are different kinds of bulbs, what is the prob

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In a bulb factory there are different kinds of bulbs, what is the prob  [#permalink]

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New post 19 Nov 2019, 01:41
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In a bulb factory there are different kinds of bulbs, what is the probability that a bulb chosen randomly is a halogen?

(1) There are three times as many halogens than any other bulb in the factory.
(2) The ratio between the halogen to all the other bulbs is 2 to 7.


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Re: In a bulb factory there are different kinds of bulbs, what is the prob  [#permalink]

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New post 19 Nov 2019, 02:09
Bunuel wrote:
In a bulb factory there are different kinds of bulbs, what is the probability that a bulb chosen randomly is a halogen?

(1) There are three times as many halogens than any other bulb in the factory.
(2) The ratio between the halogen to all the other bulbs is 2 to 7.


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#1
There are three times as many halogens than any other bulb in the factory.
total bulbs not know
x=3x ; total 3/4 halogen
insufficient
#2
The ratio between the halogen to all the other bulbs is 2 to 7.
H/other = 2/7 so P of halogen ; 2/9
IMO B sufficient
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Re: In a bulb factory there are different kinds of bulbs, what is the prob  [#permalink]

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New post 19 Nov 2019, 02:18
My answer is (D).
(1) There are three times as many halogens than any other bulb in the factory.
This indicates that the ratio between Halogens vs. others is 3:1. Sufficient
(2) It provides the ratio directly. Sufficient.

If my answer is right, though, statement (1) and (2) provides different ratios. In actual GMAT DS questions, (1) and (2) never contradict with each other.
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Re: In a bulb factory there are different kinds of bulbs, what is the prob  [#permalink]

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New post 21 Nov 2019, 06:12
1
Bunuel wrote:
In a bulb factory there are different kinds of bulbs, what is the probability that a bulb chosen randomly is a halogen?

(1) There are three times as many halogens than any other bulb in the factory.
(2) The ratio between the halogen to all the other bulbs is 2 to 7.


(1) There are three times as many halogens than any other bulb in the factory. insufic

If h=3, a=1; h/total=3/(1+3)=3/4;
If h=3, a=1, b=1; h/total=3/(1+1+3)=3/5;
Since we don't know how many kinds of bulbs there are, we cannot find the prob.

(2) The ratio between the halogen to all the other bulbs is 2 to 7. sufic

h/others=2/7…others=7h/2…total=h+others;
h/total=h/h+others=h/(h+7h/2)=h/(9h/2)=2/9.

Ans (B)
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Re: In a bulb factory there are different kinds of bulbs, what is the prob   [#permalink] 21 Nov 2019, 06:12
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