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Bunuel
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We get even numbers when 2 Odd numbers are picked or 2 even numbers are picked.

We have 3 odd numbers and 2 even numbers.

Probability that 2 odd numbers are picked (with replacement) = \(\frac{3}{5} * \frac{3}{5} = \frac{9}{25}\)

Probability that 2 even numbers are picked (with replacement) = \(\frac{2}{5} * \frac{2}{5} = \frac{4}{25}\)


Therefore the required probability = \(\frac{9}{25} + \frac{4}{25} = \frac{13}{25}\)


Option D

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blocks numbered 1, 2, 3, 4, and 5

P(E1)= When John Picks an even numbered block then Lisa has to pickup an even too = 2C1/5C1 * 2C1/5C1 = 4/25
P(E2)= When John Picks an odd numbered block then Lisa has to pickup an odd too = 3C1/5C1 * 3C1/5C1 = 9/25

P(E) = P(E1) + P(E2) = 4/25 + 9/25 = 13/25.

So, I think D. :)
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A box contains five blocks numbered 1, 2, 3, 4, and 5. John picks a block and replaces it. Lisa then picks a block. What is the probability that the sum of the numbers they picked is even?

(A) 9/25
(B) 2/5
(C) 1/2
(D) 13/25
(E) 3/5

Even + Even = Even; Even number pick up probably of John and Even number pick up probably of Lisa; \(\frac{2}{5}*\frac{2}{5}=\frac{4}{25}\)

Odd + Odd = Even; Odd number pick up probably of John and Odd number pick up probably of Lisa; \(\frac{3}{5}*\frac{3}{5}=\frac{9}{25}\)

The probability that the sum of the numbers they picked is even \(=\frac{4}{25}+\frac{9}{25}=\frac{13}{25}\)

The answer is \(D\)
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The only way that the sum of their numbers wouldn't be even is if one of them picks an even block and the other picks an odd block

the probability of this event is calculated as so:

prob that the first person picks an odd block: 3/5
prob that second person picks an even block: 2/5

3/5 * 2/5 = 6/25

prob that the first person picks an even block: 2/5
prob that the second person picks an odd block: 3/5

2/5 * 3/5 = 6/25

The inverse probability of what we are solving for is therefore: 6/25 + 6/25 = 12/25
this means that the probability we are looking for is 13/25
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