# ACT Math : How to factor a number

## Example Questions

### Example Question #1 : How To Factor A Number

The number 9 is the second smallest integer with 3 factors, 1, 3, and 9. What is the sum of the factors of the smallest integer with only 3 factors?

17
7
15
13
4
Explanation:

Here we must do two things. First we must find the smallest integer with 3 factors, then we must add those factors so that we can obtain our answer.

Looking at numbers less than 9 with only 3 factors, the only possibility is the number 4, whose factors are 1, 2, and 4.

The sum of these factors is 1 + 2 + 4 = 7

### Example Question #1 : How To Factor A Number

If a and b are both factors of 64, which of the following could be a * b?

1920

200

34

128

128

Explanation:

The factors of 64 are: 1,2,4,8,16,32,64. Therefore, 128 could be the product of 16 and 8.

### Example Question #82 : Integers

Which of the following is not a factor of 52?

Explanation:

Listing all the factors of 52: 1,2,4,13,26,52.

3 is not one of the factors.

### Example Question #83 : Integers

Which of the following lists all the factors of 36?

2, 4, 12, 18, 36

1, 2, 3, 4, 6, 9, 12, 18, 36

2, 3

36, 72

1, 36

1, 2, 3, 4, 6, 9, 12, 18, 36

Explanation:

1, 2, 3, 4, 6, 9, 12, 18, 36 are all of the factors of 36.

### Example Question #1 : Other Factors / Multiples

What are the factors of the number 12?

2, 3, 6

2, 6

1, 2, 3, 4, 6, 12

1, 12

3, 4

1, 2, 3, 4, 6, 12

Explanation:

The factors of a number are all the numbers that can be multiplied by an integer to get that number.

### Example Question #83 : Integers

What is the sum of the greatest common factor (GCF) and the least common multiple (LCM) of , , and ?

Explanation:

:  the largest factor that divides evenly into all numbers

:  the smallest non-zero number that divides evenly into all numbers.  If you are unable to find the GCF, then it is 1.

Prime factorize all numbers:

, because all numbers are relatively prime.

Therefore, .

### Example Question #7 : Other Factors / Multiples

What is the power of the greatest prime factor of ?

4

Explanation:

To get the answer to this question, just carefully prime factor the value :

First,

Now,

For , begin by dividing by :

Now, this is a bit trickier for . This happens to be divisible by :

also is divisible by :

### Example Question #8 : Other Factors / Multiples

How many factors are there for the number ?

Explanation:

To find the number of factors of a given number, the easiest thing to do is to make a table of the factors, starting with  and that number. So, for , we get:

At this point, things begin to repeat. Thus, the total number of factors is .

### Example Question #2 : Other Factors / Multiples

What is the median value of the factors of ?