PSAT Math : Statistics

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #6 : How To Find Range

The median of a set of eleven consecutive odd integers is 39. What is the range of the set?

Possible Answers:

10

39

20

29

30

Correct answer:

20

Explanation:

Let's represent the eleven integers as A, B, C, D, E, F, G, H, I, J, and K. Let's assume that if we lined them up from least to greatest, the set would be as follows:

A, B, C, D, E, F, G, H, I, J, K

The median in this set is the middle number. In this case, the middle number will always be F, because there are five numbers before it and five numbers after it.

We are told that the median is 39. Thus F = 39, and our set looks like this:

A, B, C, D, E, 39, G, H, I, J, K

Since we know that all the numbers are consecutive odd integers, the set must consist of the five odd numbers before 39 and the five odd numbers after 39. In other words, the set is this:

29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49

The question asks for the range of the set, which is the difference between the largest and smallest numbers. In this case, the range is 49 – 29 = 20.

The answer is 20.

Example Question #3 : How To Find Range

Find the range.

\dpi{100} \small 9,6,1,6,5,9,8,3

Possible Answers:

\dpi{100} \small 6

\dpi{100} \small 5

\dpi{100} \small 8

\dpi{100} \small 4

\dpi{100} \small 7

Correct answer:

\dpi{100} \small 8

Explanation:

First, arrange the numbers from highest to lowest, then subtract the highest number from the lowest number.

Example Question #1 : How To Find Range

Marker Colors

Students

Blue

13

Pink

10

Orange

5

Brown

5

Green

7

The above chart shows the number of students in a class who chose each of the five marker colors available.

What is the range of the students’ choices?

Possible Answers:

Correct answer:

Explanation:

The range of a data set is the distance between the smallest number and the largest number. To find the range, you subtract the smallest number (5) from the largest number (13). Therefore, the range is 8.

Example Question #1 : How To Find Range

Find the range of the following set of numbers:

Possible Answers:

Correct answer:

Explanation:

To find the range of a data set, subtract the smallest number in the set from the largest:

Example Question #1 : How To Find The Probability Of An Outcome

A bag of marbles has 7 yellow marbles, 5 red marbles, 3 blue marbles, and 6 white marbles. What is the probability of choosing a yellow marble, putting it back and choosing a blue marble, and then NOT putting the blue marble back and picking a white marble?

Possible Answers:

8/31

2/3

1/9

3/17

1/70

Correct answer:

1/70

Explanation:

There are a total of 7 + 5 + 3 + 6 = 21 marbles. The probability of picking a yellow marble is 7/21 = 1/3. Then we put it back and choose a blue marble with probability 3/21 = 1/7. We do NOT put this blue marble back, but then we grab for a white. The probability of picking a white is now 6/20 = 3/10, because now we are choosing from 20 marbles instead of 21. So putting it together, the probability of choosing a yellow marble, replacing it and then choosing a blue and a white, is 1/3 * 1/7 * 3/10 = 1/70.

Example Question #1 : How To Find The Probability Of An Outcome

A bag of jellybeans has 20 watermelon jellybeans, 45 sour apple jellybeans, 30 orange jellybeans and 5 cotton candy jellybeans.  If you reach in and grab one jelly bean, what is the probability that it will be watermelon flavored?

Possible Answers:

1/20

1/3

1/4

4/19

1/5

Correct answer:

1/5

Explanation:

Add up the total number of jellybeans, 20 + 45 + 30 + 5 = 100. 

Divide the number of watermelon jellybeans by the total: 20/100 and reduce the fraction to 1/5.

Example Question #131 : How To Find The Probability Of An Outcome

You went to order a cake but all of the cakes are in identical boxes. If there are five chocolate cakes, four carrot cakes, three vanilla cakes, and six red velvet cakes, what is the maximum number of boxes that you would have to open to ensure that you have one of each type of cake?

Possible Answers:

4

16

12

9

Correct answer:

16

Explanation:

There are four different types of cake. In this type of problem we want to guarantee we have one of each, so we need to assumbe we have very bad luck. We start with the red velvet since that is the type with the most cakes. If we open those 6 we are not guaranteed to have different ones. Then say we opened all five chocolate cakes, then all four carrot cakes. We still have only three types of cakes but opened 15 boxes. When we open the next box (16) we will be guaranteed to have one of each.

 

 

 

Example Question #1 : How To Find The Probability Of An Outcome

A circle is inscribed inside a square. If a point inside the square is selected at random, what is the probability that the point will also be inside the circle?

Possible Answers:

5/6

3/4

π/6

π/4

Correct answer:

π/4

Explanation:

The probability of the point being inside the circle is the ratio of the area of the circle to the area of the square. If we suppose that the circle has radius r, then the square must have side 2r. The area of the circle is πr2 and the area of the square is 〖(2r)〗2=〖4r〗2, so the proportion of the areas is (πr2)/〖4r〗2  =π/4.

Example Question #1 : How To Find The Probability Of An Outcome

John has a bowl with 54 marbles in it. Half of the marbles are green and half of the marbles are blue. John takes 3 green marbles and 6 blue marbles from the jar. John then takes 13 additional marbles from the remaining marbles in the jar. What is the minimum number of these 13 marbles that must be green in order for there to be more blue marbles than green marbles left?

Possible Answers:

8

9

10

5

4

Correct answer:

9

Explanation:

The bowl has 54 marbles, half green and half blue. This gives us 27 green and 27 blue marbles:

27 G / 27 B

John then takes 3 green and 6 blue from the bowl. This leaves the bowl with:

24 G / 21 B

If there are going to be more blue than green marbles after John's 13 marbles, he has to take at least 4 more green marbles than blue marbles, because right now there are 3 less blue marbles. Therefore, we need to take at least 9 green marbles, which would mean 4 or less of the marbles would be blue (8 green and 5 blue would leave us with equal green and equal blue marbles, so it would have to be more than 8 green marbles, which gives us 9 green marbles).

We can also solve this as an inequality. You take the difference in marbles, which is 3, which means you need the difference in green and blue marbles to be greater than 3, or at least 4. You have b + g = 13 and g - b > 3, where b and g are positive integers.

b + g = 13 (Subtract g on both sides of the equation)

b = 13 - g

g - b > 3 (Substitute above equation)

g - (13 - g) > 3 (Distribute negative sign in parentheses)

g - 13 + g > 3 (Add both g variables)

2g - 13 > 3 (Add 13 to both sides of the inequality)

2g > 16 (Divide both sides of the inequality by 2)

g > 8 so g has to be 9 or greater.

Example Question #1 : How To Find The Probability Of An Outcome

If x is chosen at random from the set (4, 6, 7, 9, 11) and y is chosen at random from the set (12, 13, 15, 17) then what is the probability that xy is odd?

Possible Answers:

9/20

11/20

3/10

6/10

9/10

Correct answer:

9/20

Explanation:

If x is chosen at random from the set (4, 6, 7, 9, 11) and y is chosen at random from the set (12, 13, 15, 17) then what is the probability that xy is odd?

Here we have 5 possible choices for x and 4 possible choices for y, giving us 5 * 4 = 20 possible outcomes.

We know that odd times odd = odd; even times even = even; and even times odd = even. Thus we need all of the outcomes where x and y are odd. We have 3 possibilities of odd numbers for x, and 3 possibilities of odd numbers for y, so we will have 9 outcomes of our total 20 outcomes where xy is odd, giving us a probability of 9/20.

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