Problem Solving

AAPL wrote:Magoosh

A: {71,73,79,83,87}
B:{57,59,61,67}

If one number is selected at random from set A, and one number is selected at random from set B, what is the probability that both numbers are prime?

$$A.\ \frac{9}{20}$$
$$B.\ \frac{3}{5}$$
$$C.\ \frac{3}{4}$$
$$D.\ \frac{4}{5}$$
$$E.\ 1$$

OA B

Number of elements in Set A: {71, 73, 79, 83, 87} = 5; Number of primes in Set A = 4 (71, 73, 79, 83)

Thus, the probability of choosing a prime number from Set A = 4/5

Number of elements in Set B: B:{57, 59, 61, 67} = 4; Number of primes in Set B = 3 (53, 61, 67)

Thus, the probability of choosing a prime number from Set B = 3/4

The probability that both numbers are prime = 4/5 * 3/4 = 3/5.

The correct answer: B

Hope this helps!

-Jay
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AAPL wrote:Magoosh

A: {71,73,79,83,87}
B:{57,59,61,67}
If one number is selected at random from set A, and one number is selected at random from set B, what is the probability that both numbers are prime?
$$A.\ \frac{9}{20}$$
$$B.\ \frac{3}{5}$$
$$C.\ \frac{3}{4}$$
$$D.\ \frac{4}{5}$$
$$E.\ 1$$
OA B

There are 4 prime numbers in set A (71, 73, 79, 83) and 3 prime numbers in set B (59, 61, 67).

Thus, the probability of selecting a prime in both sets is 4/5 x 3/4 = 3/5.

Answer: B