Suppose there are 25 pieces of paper in a box, labelled with the numbers 1 to 25. Imagine picking one of the numbers at random, without looking. The diagram below groups the possible outcomes into odd numbers and multiples of 4.

One of your classmates is calculating the probability that the number we pick will be odd and a multiple of 4. But they made a mistake in their calculation.

Which of the statements below describes your classmate's mistake?

Question

Suppose there are 25 pieces of paper in a box, labelled with the numbers 1 to 25. Imagine picking one of the numbers at random, without looking. The diagram below groups the possible outcomes into odd numbers and multiples of 4.

One of your classmates is calculating the probability that the number we pick will be odd and a multiple of 4. But they made a mistake in their calculation.                                      
 
 Which of the statements below describes your classmate's mistake?

Answer

The sample size is wrong. The denominator should be 19.

Answer

She picked the wrong outcomes. The numerator should be the difference 7.

Answer

There is no mistake.

Answer

She included too many outcomes. Only the outcomes in both circles should be counted, so the numerator should be 0.

Crowdly

Suppose there are 25 pieces of paper in a box, labelled with the numbers 1 to 25...

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