PSAT Math : PSAT Mathematics

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Find Proportion

x and y are integers such that x > 0 and y > 0 .

12x + 3y = 176,500.

Quantity A: The maximum possible value of x

Quantity B: The maximum possible value of y

Possible Answers:

The relationship cannot be determined from the information given

Quantity A is greater

Quantity B is greater

The two quantities are equal

Correct answer:

Quantity B is greater

Explanation:

Note that it is not necessary to find the solution to this problem. Thus, find an expression for x and an expression for y at their maximums and compare.

First, observe from the equation that x gets smaller as y gets bigger and y gets smaller as y gets bigger. This can be found by making the equation in the form (y = mx + b) and finding that m is negative. Thus there is a negative correlation between x and y.

Therefore at its maximum, x is such that y = 0. In other words, 

  x = 176,500 / 12

y is maximum when x = 0. In other words, 

  y = 176,500 / 3

Note that 176,500 / 3 > 176,500 / 12 because the denominator is smaller. 

Example Question #92 : Fractions

If 1015 meters = 1 petameter and 1018 meters = 1 exameter, how many petameters are equal to 1 exameter?

Possible Answers:
0.1
10000
100
0.01
1000
Correct answer: 1000
Explanation:

The problem gives us two conversion ratios, which are (1018 meters/ 1 exameter) and (1 petameter/ 1015 meters).

We convert 1 exameter into petameters by multiplying 1 exameter by the conversion ratios so that all units other than petameters cancel out: 1 exameter * (1018 meters/ 1 exameter) * (1 petameter/ 1015 meters). Therefore one exameter is 1018/1015  petameters. Finally, when dividing terms with common bases, we subtract the exponents, so our result is 1018/1015 = 103 = 1000.

Example Question #1 : How To Find Proportion

If Shaquille O'Neal is 7 feet tall and casts a shadow 5 feet long. At the same time of day, how long would the shadow be from a 49-foot tall house?

Possible Answers:

15

55

35

25

45

Correct answer:

35

Explanation:

The question is about similar triangles. The height of the two objects would correspond with each other and the shadows would correspond with each other. As with many geometry problems, it is helpful if you draw a diagram.  Set up a proportion for each so the height of Shaquille O'Neal to the height of the house then his shadow to the shadow of the house.

7/49 = 5/x

Solve for x by cross-multiplying:

5 * 49 = 7x

x = 35

Example Question #1 : How To Find Proportion

John is 35 years old, 5 years older than his brother Bob and 20 years younger than his father Jack.  How old was Jack when Bob was born?

Possible Answers:

25

5

35

28

20

Correct answer:

25

Explanation:

If John is 35, that means currently Jack is 55 and Bob is 30.  55 – 30 = 25 years old when Bob was born.

Example Question #62 : Proportion / Ratio / Rate

In a mixture of flour and sugar, the ratio of flour to sugar is 5 to 1. How many kilograms of flour will there be in 12 kilograms of this mixture?

Possible Answers:

5

4

2

3

1

Correct answer:

2

Explanation:

The question says that the mixture has 5 units of flour for every 1 unit of sugar, which adds up to a total of 5 + 1 = 6 units of the mixture; therefore in 6 kilograms of the mixture, 1 kilogram will be sugar.

To find how much sugar will be in 12 kilograms of the mixture, we multiply the amount of sugar in 6 kilograms of the mixture by 2, giving us 1 kilogram of sugar * 2 = 2 kilograms of sugar.

Example Question #63 : Proportion / Ratio / Rate

A survey of studio offices in a city with 14,000 employees reveals that there are, on average, 12.5 employees per office. If there have been a cumulative total of 3,400 printers sold to the offices of the city, what is the best estimate of the average number of printers per office?

Possible Answers:

0.77

4.1

1.2

3.0

0.33

Correct answer:

3.0

Explanation:

The best estimate would be to simply divide the number of printers by the number of offices. However, they only gave us the average number of employees per office, thus to find the number of offices we divide:

14,000 (people)/12.5 (per office) = 14,000/12.5 = 1,120 offices

We already know the number of printers available total, thus again divide

3,400 (printers)/1,120 (offices) = 3.04, or 3.0 printers per office as the best estimate.

Example Question #101 : Fractions

A factory makes six widgets in a batch that takes 24 minutes to complete. How long does it take to make 57 widgets?

Possible Answers:

4 hours

3 hours, 45 minutes

3 hours, 30 minutes

3 hours

3 hours, 5 minutes

Correct answer:

4 hours

Explanation:

We have here a basic ratio:

6/24 = 57/x

Solving for x, we get: 6x = 24 * 57; 6x = 1368; x = 228

Now, we must be very careful here, however. Is 228 an even multiple of 24?  228/24 = 9.5.  That means that we would have to do 9.5 batches.  The question indicates that these are batched in groups of 6; therefore, we have to run 10 batches to get our amount. That would be 240 minutes or 4 hours.

Example Question #561 : Arithmetic

Kendall can run 26 miles in 4 hours and 20 minutes. At this rate how long would it take him to run 100 miles?

Possible Answers:

10 hours and 55 minutes

16 hours and 40 minutes

12 hours and 20 minutes

18 hours and 35 minutes

15 hours and 50 minutes

Correct answer:

16 hours and 40 minutes

Explanation:

Set up a proportion and conver 4 hours and 20 minutes into just minutes for now,

so 26/260 = 100/X

Solve for X = 1000 minutes

1000/60 = 16 hours and 40 minutes

Example Question #562 : Arithmetic

A recipe calls for a ratio of  for wheat, barley, and flour. If we have 12 pounds of barley, how much wheat do we need to use all of it?

Possible Answers:

Correct answer:

Explanation:

We can set up a ratio of  and then solve for

Example Question #71 : Fractions

To ship a package, the postal service charges  for the first 150 grams and  for each additional 50 grams or part thereof. What is one possible weight in grams for a package that costs  to ship?

Possible Answers:

Correct answer:

Explanation:

The weight will be 150 grams + (1.15 – 0.55)/0.05 * 50g.

You need to subtract first 150 grams cost from the total cost and divide by the price per unit to determine how many units. Next, multiply units by weight per unit and add to the original first 150 grams.

 150 + 600 = 750 grams

This is the maximum weight that can be sent at that price; the minimum weight that could be charged this price would be 701 grams. Hence a package weighing 750 grams will be charged $1.15.

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