All PSAT Math Resources
Example Questions
Example Question #52 : Calculating Discrete Probability
Set A:
Set B:
One letter is picked from Set A and Set B. What is the probability of picking at least one consonant?
Set A:
Set B:
In Set A, there are five consonants out of a total of seven letters, so the probability of drawing a consonant from Set A is .
In Set B, there are three consonants out of a total of six letters, so the probability of drawing a consonant from Set B is .
The question asks for the probability of drawing at least one consonant, which can be interpreted as a union of events. To calculate the probability of a union, sum the probability of each event and subtract the intersection:
The interesection is:
So, we can find the probability of drawing at least one consonant:
Example Question #42 : Data Analysis / Probablility
Set A:
Set B:
One letter is drawn from Set A, and one from Set B. What is the probability of drawing a matching pair of letters?
Set A:
Set B:
Between Set A and Set B, there are two potential matching pairs of letters: AA and XX. The amount of possible combinations is the number of values in Set A, multiplied by the number of values in Set B, .
Therefore, the probability of drawing a matching set is:
Example Question #164 : Data Analysis
In a particular high school, 200 students are freshmen, 150 students are sophomores, 250 students are juniors, and 100 students are seniors. Twenty percent of freshmen are in honors classes, ten percent of sophomores are in honors classes, twelve percent of juniors are in honors classes, and thirty percent of seniors are in honors classes.
If a student is chosen at random, what is the probability that that student will be a student who attends honors classes?
First calculate the number of students:
The probability of drawing an honors student will then be the total number of honors students divided by the total number of students attending the school:
Example Question #61 : Discrete Probability
In a particular high school, 200 students are freshmen, 150 students are sophomores, 250 students are juniors, and 100 students are seniors. Twenty percent of freshmen are in honors classes, ten percent of sophomores are in honors classes, twelve percent of juniors are in honors classes, and thirty percent of seniors are in honors classes.
If a student is chosen at random, what is the probability that that student will be a senior student and a student who does not attend honors classes?
First calculate the number of students:
The percentage of seniors that do not attend honors classes is:
Therefore, the probability of selecting a student who is a senior and one who does not attend honors classes is:
Example Question #101 : Probability
11 cards are placed into a box numbered 5 - 15. If one card is randomly drawn from the box, what is the probabiltiy that a prime number will be on the card?
3/5
2/5
6/11
1/2
4/11
4/11
Possible numbers 5,6,7,8,9,10,11,12,13,14,15 (11 total numbers)
Prime numbers are 5,7,11,13 (4 total prime numbers)
totalnumber of prime numbers/ total numbers in box
Answer = 4/11
Example Question #111 : Outcomes
Aaron, Gary, Craig, and Boone are sitting down in a row of four chairs. What is the probability that Aaron and Gary will be seated beside each other?
Consider first all of the possible ways the men may be arranged, which is
Now, consider all of the ways that Aaron and Gary could be seated beside each other; it may be easier to visualize by drawing it out:
- A G _ _
- G A _ _
- _ A G _
- _ G A _
- _ _ A G
- _ _ G A
As seen, there are six possibilities.
Finally, for each of these cases, Craige and Boone could be seated in one of two ways.
So the probability that Aaron and Gary will be seated beside each other is:
Example Question #1 : Proportion / Ratio / Rate
A cafeteria with 40 tables can sit 600 people. Some tables can sit 10 people and some can sit 20 people. What is the ratio of the number of 10-person tables to the number of 20-person tables?
2:1
1:1
4:1
1:2
1:4
1:1
Let x be the number of 10-person tables, and y be the number of 20-person tables. Since there are 40 tables in the cafeteria, x + y = 40. 10x represents the number of people sitting at 10-person tables, and 20y represents the number of people sitting at 20-person tables. Since the cafeteria can seat 600 people, 10x + 20y = 600. Now we have 2 equations and 2 unknowns, and can solve the system. To do this, multiply the first equation by 10 and subtract it from the second equation. This yields 0x + 10y = 200; solving for y tells us there are 20 tables that seat 20 people. Since x + y = 40, x = 20, so there are 20 tables that seat 10 people. The ratio of x:y is therefore 1:1.
Example Question #1 : Proportion / Ratio / Rate
The first term in a sequence is m. If every term thereafter is 5 greater than 1/10 of the preceding term, and m≠0, what is the ratio of the second term to the first term?
(m+5)/10
(m+50)/10m
(m+10)/50m
(m+10)/5
(m+50)/10m
The first term is m, so the second term is m/10+5 or (m+50)/10. When we take the ratio of the second term to the first term, we get (((m+50)/10))/m, which is ((m+50)/10)(1/m), or (m+50)/10m.
Example Question #2 : How To Find A Ratio
Two cars were traveling 630 miles. Car A traveled an average speed of 70 miles per hour. If car B traveled 90 miles an hour, how many miles had car A traveled when car B arrived at the destination?
700
490
630
140
490
We first divide 630 miles by 90 miles per hour to get the amount of time it took car B to reach the destination, giving us 7 hours. We then multiply 7 hours by car A’s average speed and we get 490 miles.
Example Question #1 : Proportion / Ratio / Rate
STUDENT ATHLETES WHO USE STEROIDS |
|||
|
MEN |
WOMEN |
TOTAL |
BASKETBALL |
A |
B |
C |
SOCCER |
D |
E |
F |
TOTAL |
G |
H |
I |
In the table above, each letter represents the number of students in each category. Which of the following must be equal to I?
A+B
A+D
A+D+G
G+H
G+H
Since G is the total number of male athletes that use steroids and H is the total number of female athletes that use steroids, the sum of the two is equal to I, which is the total number of all students using steroids.