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

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by BTGmoderatorDC » Wed Nov 20, 2019 5:39 pm
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

OA B

Source: Manhattan Prep
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by Jay@ManhattanReview » Wed Nov 20, 2019 9:33 pm
BTGmoderatorDC 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

OA B

Source: Manhattan Prep
Given that there are 5 snakes that have no stripes and are not poisonous, there are 30 - 5 = 25 snakes that either have stripes or are poisonous.

Say,

there are x snakes that have stripes and are poisonous. Thus,
there are (10 - x) snakes that have stripes but are not poisonous, and
there are (21 - x) snakes that are poisonous but do not have stripes.

=> 25 = (21 - x) + (10 - x) + x
=> x = 6

The correct answer: B

Hope this helps!

-Jay
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by swerve » Thu Nov 21, 2019 5:54 am
BTGmoderatorDC 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

OA B

Source: Manhattan Prep
Total \(= a +b -\) both \(+\) neither

\(30= 10 + 21 - x + 5\)

\(x = 6\). Answer B
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by Scott@TargetTestPrep » Wed Nov 27, 2019 10:44 am
BTGmoderatorDC 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

OA B

Source: Manhattan Prep
We can create the equation:

Total = #Stripes + #Poisonous - Both + Neither

30 = 10 + 21 - Both + 5

30 = 36 - Both

Both = 6

Answer: B

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