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# Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,

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Math Expert
Joined: 02 Sep 2009
Posts: 59722
Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 02:12
00:00

Difficulty:

5% (low)

Question Stats:

88% (01:09) correct 12% (01:39) wrong based on 119 sessions

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Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Kudos for a correct solution.

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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 02:18
[quote="Bunuel"]Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Solution -

Total = Stripes + Poisonous - Both + Neither
30 = 10 + 21 + 5 - Both - > Both = 6

the snakes have both stripes AND are poisonous = 6
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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 02:36
1
You do not need a grid

A + B - Both + Neither

10+21-B+5=30

B=6

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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 04:05
Bunuel wrote:
Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Kudos for a correct solution.

In My opinion, Such questions can be best slved by Bouble Matrix Method

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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 05:03
1
Bunuel wrote:
Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Kudos for a correct solution.

Total = a +b - both + neither

30= 10 + 21 - x + 5

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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 05:14
Total = 30 = T

Let snakes with stripes be X, and snakes that are poisonous be Y. Snakes that have neither stripes nor are poisonous be Z.

X (AND) Y = (X + Y) - (T - Z) = (10+21) - (30-5) = 31-25 = 6.
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Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 07:28
1
$$30 = 10 + 21 + 5 - Double$$
$$Double = 6$$

For the seemingly easy questions, I also try to work through logically the answers (even though I already have the answer):

A. 4 if neither include 5 and non-poisonous total is 9, then both cannot be less than 6
B. 6 True.
C. 9 if neither include 5 and non-poisonous total is 9, then both cannot be higher than 6
D. 15 Not true. It cannot be greater than number of the snakes that have stripes
E. 20 Not true. It cannot be greater than number of the snakes that have stripes

B.
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Posts: 8309
Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 18:32
Bunuel wrote:
Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Kudos for a correct solution.

....p.....np
s..6.....4.....10
ns.15..5.....20
t...21..9......30
ans 6 B
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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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01 Jul 2015, 19:04
1
Bunuel wrote:
Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Kudos for a correct solution.

Set up a 2X2 grid to solve this question:

\begin{tabular}{| l | l | l | l |}
\hline
& Stripe & Not Stripe & Total \\ \hline
Poisonous & 6 & 15 & 21 \\ \hline
Not Poisonous & 4 & 5 & 9\\ \hline
Total & 10 & 20 & 30 \\
\hline
\end{tabular}
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Joined: 02 Sep 2009
Posts: 59722
Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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06 Jul 2015, 03:54
Bunuel wrote:
Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Kudos for a correct solution.

MANHATTAN GMAT OFFICIAL SOLUTION:

Use a Double-Set Matrix to solve this problem. First, fill in the numbers given in the problem: 30 snakes, 10 with stripes (and therefore 20 without), 21 that are poisonous (and therefore 9 that are not), and 5 that are neither striped nor poisonous. Use subtraction to fill in the rest of the chart. Thus, 6 snakes have stripes and are poisonous.

Attachment:

2015-07-06_1452.png [ 10.19 KiB | Viewed 2435 times ]

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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,  [#permalink]

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24 Nov 2019, 07:24
Bunuel wrote:
Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous, and 5 have no stripes and are not poisonous. How many of the snakes have stripes AND are poisonous?

A. 4
B. 6
C. 9
D. 15
E. 20

Kudos for a correct solution.

We can create the equation:

Total = #Stripes + #Poisonous - Both + Neither

30 = 10 + 21 - Both + 5

30 = 36 - Both

Both = 6

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Re: Of 30 snakes at the reptile house, 10 have stripes, 21 are poisonous,   [#permalink] 24 Nov 2019, 07:24
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