All PSAT Math Resources
Example Questions
Example Question #2 : How To Multiply Even Numbers
Let a and b be positive integers such that ab2 is an even number. Which of the following must be true?
I. a2 is even
II. a2b is even
III. ab is even
I and II only
I only
II and III only
I, II, and III
II only
II and III only
In order to solve this problem, it will help us to find all of the possible scenarios of a, b, a2, and b2. We need to make use of the following rules:
1. The product of two even numbers is an even number.
2. The product of two odd numbers is an odd number.
3. The product of an even and an odd number is an even number.
The information that we are given is that ab2 is an even number. Let's think of ab2 as the product of two integers: a and b2.
In order for the product of a and b2 to be even, at least one of them must be even, according to the rules that we discussed above. Thus, the following scenarios are possible:
Scenario 1: a is even and b2 is even
Scenario 2: a is even and b2 is odd
Scenario 3: a is odd and b2 is even
Next, let's consider what possible values are possible for b. If b2 is even, then this means b must be even, because the product of two even numbers is even. If b were odd, then we would have the product of two odd numbers, which would mean that b2 would be odd. Thus, if b2 is even, then b must be even, and if b2 is odd, then b must be odd. Let's add this information to the possible scenarios:
Scenario 1: a is even, b2 is even, and b is even
Scenario 2: a is even, b2 is odd, and b is odd
Scenario 3: a is odd, b2 is even, and b is even
Lastly, let's see what is possible for a2. If a is even, then a2 must be even, and if a is odd, then a2 must also be odd. We can add this information to the three possible scenarios:
Scenario 1: a is even, b2 is even, and b is even, and a2 is even
Scenario 2: a is even, b2 is odd, and b is odd, and a2 is even
Scenario 3: a is odd, b2 is even, and b is even, and a2 is odd
Now, we can use this information to examine choices I, II, and III.
Choice I asks us to determine if a2 must be even. If we look at the third scenario, in which a is odd, we see that a2 would also have to be odd. Thus it is possible for a2 to be odd.
Next, we can analyze a2b. In the first scenario, we see that a2 is even and b is even. This means that a2b would be even. In the second scenario, we see that a2 is even, and b is odd, which would still mean that a2b is even. And in the third scenario, a2 is odd and b is even, which also means that a2b would be even. In short, a2b is even in each of the possible scenarios, so it must always be even. Thus, choice II must be true.
We can now look at ab. In scenario 1, a is even and b is even, which means that ab would also be even. In scenario 2, a is even and b is odd, which means that ab is even again. And in scenario 3, a is odd and b is even, which again means that ab is even. Therefore, ab must be even, and choice III must be true.
The answer is II and III only.
Example Question #3 : How To Multiply Even Numbers
Let equal the product of two numbers. If , then the two numbers COULD be which of the following?
8 and 8
2 and 8
20 and 4
0 and 16
32 and 2
2 and 8
The word "product" refers to the answer of a multiplication problem. Since 2 times 8 equals 16, it is a valid pair of numbers.
Example Question #4 : How To Multiply Even Numbers
If and is an odd integer, which of the following could be divisible by?
If is an odd integer then we can plug 1 into and solve for yielding 13. 13 is prime, meaning it is only divisible by 1 and itself.
Example Question #1 : How To Multiply Even Numbers
is even
is even
Therefore, which of the following must be true about ?
It must be odd.
It must be even.
It could be either even or odd.
It could be either even or odd.
Recall that when you multiply by an even number, you get an even product.
Therefore, we know the following from the first statement:
is even or is even or both and are even.
For the second, we know this:
Since is even, therefore, can be either even or odd. (Regardless of what it is, we can get an even value for .)
Based on all this data, we can tell nothing necessarily about . If is even, then is even, even if is odd. However, if is odd while is even, then will be even.
Example Question #3 : How To Multiply Even Numbers
In a group of philosophers, are followers of Durandus. Twice that number are followers of Ockham. Four times the number of followers of Ockham are followers of Aquinas. One sixth of the number of followers of Aquinas are followers of Scotus. How many total philosophers are in the group?
In a group of philosophers, are followers of Durandus. Twice that number are followers of Ockham. Four times the number of followers of Ockham are followers of Aquinas. One sixth of the number of followers of Aquinas are followers of Scotus. How many total philosophers are in the group?
To start, let's calculate the total philosophers:
Ockham: * <Number following Durandus>, or
Aquinas: * <Number following Ockham>, or
Scotus: divided by , or
Therefore, the total number is:
Example Question #1 : How To Multiply Even Numbers
If n is an integer that is not equal to 0, which of the following must be greater than or equal to n?
I. 7n
II. n + 5
III. n2
II and III only
I and III only
I, II, and III
I and II only
II only
II and III only
I is not always true because a negative number multiplied by 7 will give a number that is more negative than the original. II is true because adding 5 to any number will increase the value. III is true because squaring any number will increase the magnitude of the value, and squaring a negative number will make it positive.
Example Question #1 : How To Multiply Even Numbers
Which of the following integers has an even integer value for all positive integers and ?
There are certain patterns that can be used to predict whether the product or sum of numbers will be odd or even. The sum of two odd numbers is always even, as is the sum of two even numbers. The sum of an odd number and an even number is always odd. In multiplication the product of two odd numbers is always odd. While the product of even numbers, as well as the product of odd numbers multiplied by even numbers is always even. So for this problem we need to find scenarios where the only possibile answers are even. can only result in even numbers no matter what positive integers are used for and , because must can only result in even products; the same can be said for . The rules provide that the sum of two even numbers is even, so is the answer.
Example Question #1582 : Sat Mathematics
How many positive integers less than ten thousand are multiples of both eight and eighteen?
139
138
555
70
72
138
In order to find all of the numbers that are multiples of both 8 and 18, we need to find the least common mutliple (LCM) of 8 and 18. The easiest way to do this would be to list out the multiples of 8 and 18 and determine the smallest one that is common to both.
First, let's list the first several multiples of eight:
8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88 . . .
Next, we list the first several multiples of eighteen:
18, 36, 54, 72, 90, 108, 126, 144 . . .
By comparing the multiples of eight and eighteen, we can see that the smallest one that they share is 72. Thus, the LCM of 8 and 18 is 72.
Because the LCM is 72, this means that every multiple of 72 is also a multiple of both 8 and 18. So, in order to find all of the multiples less than ten thousand that are both multiples of 8 and 18, we simply need to find how many multiples of 72 are less than 10000, and to do this, all we have to do is to divide 10000 by 72.
When we divide 10000 by 72, we get 138 with a remainder of 64; therefore, 72 will go into ten thousand 138 times before it exceeds ten thousand. In other words, there are 138 numbers less than 10000 that are multiples of 72 and, by extension, also multiples of both 8 and 18.
The answer is 138.
Example Question #1 : Factors / Multiples
If is divisible by 2, 4 and 7, which of the following is a possible value of ?
136
172
154
168
114
168
The simplest way to solve this question is to go through each answer choice and check to see if it is divisible by 2, 4 and 7. When we do this, we find that only 168 is evenly divisible by each of these numbers. 114 is not divisible by 4 or 7, 172 is not divisibly by 7, 136 is not divisble by 7, and 154 is not divisible by 4.
Example Question #11 : Least Common Multiple
If a, b, and c are positive integers such that 4a = 6b = 11c, then what is the smallest possible value of a + b + c?
33
132
67
11
121
67
We are told that a, b, and c are integers, and that 4a = 6b = 11c. Because a, b, and c are positive integers, this means that 4a represents all of the multiples of 4, 6b represents the multiples of 6, and 11c represents the multiples of 11. Essentially, we will need to find the least common multiples (LCM) of 4, 6, and 11, so that 4a, 6b, and 11c are all equal to one another.
First, let's find the LCM of 4 and 6. We can list the multiples of each, and determine the smallest multiple they have in common. The multiples of 4 and 6 are as follows:
4: 4, 8, 12, 16, 20, ...
6: 6, 12, 18, 24, 30, ...
The smallest multiple that 4 and 6 have in common is 12. Thus, the LCM of 4 and 6 is 12.
We must now find the LCM of 12 and 11, because we know that any multiple of 12 will also be a multiple of 4 and 6.
Let's list the first several multiples of 12 and 11:
12: 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, ...
11: 11, 22, 33, 44, 55, 66, 77, 88, 99, 110, 121, 132, ...
The LCM of 12 and 11 is 132.
Thus, the LCM of 4, 6, and 12 is 132.
Now, we need to find the values of a, b, and c, such that 4a = 6b = 12c = 132.
4a = 132
Divide each side by 4.
a = 33
Next, let 6b = 132.
6b = 132
Divide both sides by 6.
b = 22
Finally, let 11c = 132.
11c = 132
Divide both sides by 11.
c = 12.
Thus, a = 33, b = 22, and c = 12.
We are asked to find the value of a + b + c.
33 + 22 + 12 = 67.
The answer is 67.