In a collection of 80 cards, each card is labeled with a unique integer from 1 to 80. If Alex randomly selects one card, puts it back, and then selects another card, what is the probability that the product of the two integers on the selected cards is odd?

Answer Choices

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1/10

1/4

Correct

1/2

3/5

7/8

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Explanation

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Official Explanation

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The product of the two cards will be ODD if both selected cards are odd. There are 40 odd cards and 40 even cards in total. The probability of drawing the first odd card is

\frac{40}{80}

. Since…

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Comments

PhilemonAug 28, 2024

thanksss

DivyankaFeb 9, 2024

Great

What this question tests

What it tests

Your ability to compute probabilities of single and compound events, including 'at least one' questions.

Common trap

Forgetting to use the complement for 'at least one', or treating dependent events as independent.