PSAT Math : PSAT Mathematics

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #3 : How To Divide Exponents

If , then

 

Possible Answers:

Cannot be determined

Correct answer:

Explanation:

Start by simplifying the numerator and denominator separately. In the numerator, (c3)2 is equal to c6. In the denominator, c2 * c4 equals c6 as well. Dividing the numerator by the denominator, c6/c6, gives an answer of 1, because the numerator and the denominator are the equivalent.

 

Example Question #3 : How To Divide Exponents

If , which of the following is equal to ?

Possible Answers:

a4

The answer cannot be determined from the above information

a18

a

a6

Correct answer:

a18

Explanation:

The numerator is simplified to  (by adding the exponents), then cube the result. a24/a6 can then be simplified to .

Example Question #3 : How To Divide Exponents

Possible Answers:

\dpi{100} \small 343

\dpi{100} \small 28

\dpi{100} \small 7

\dpi{100} \small 42

\dpi{100} \small 49

Correct answer:

\dpi{100} \small 7

Explanation:

The easiest way to solve this is to simplify the fraction as much as possible. We can do this by factoring out the greatest common factor of the numerator and the denominator. In this case, the GCF is 

Now, we can cancel out the  from the numerator and denominator and continue simplifying the expression.

Example Question #1 : Exponents

If (300)(400) = 12 * 10n, n =

Possible Answers:

12

3

7

4

2

Correct answer:

4

Explanation:

(300)(400) = 120,000 or 12 * 104.

Example Question #2 : Exponents

(2x103) x (2x106) x (2x1012) = ?

Possible Answers:

8x1023

6x1021

8x1021

6x1023

Correct answer:

8x1021

Explanation:

The three two multiply to become 8 and the powers of ten can be added to become 1021.

Example Question #65 : Exponents

Which of the following is equivalent to 

Possible Answers:

Correct answer:

Explanation:

 and  can be multiplied together to give you  which is the first part of our answer. When you multiply exponents with the same base (in this case, ), you add the exponents. In this case,  should give us  because . The answer is 

Example Question #2 : Exponents

If 3x = 27, then 22x = ?

Possible Answers:

32

64

9

8

3

Correct answer:

64

Explanation:
  1. Solve for x in 3x = 27. x = 3 because 3 * 3 * 3 = 27.
  2. Since x = 3, one can substitute x for 3 in 22x 
  3. Now, the expression is 22*3
  4. This expression can be interpreted as 22 * 2* 22. Since 22 = 4, the expression can be simplified to become 4 * 4 * 4 = 64.
  5. You can also multiply the powers to simplify the expression. When you multiply the powers, you get 26, or 2 * 2 * 2 * 2 * 2 * 2
  6. 2= 64.

Example Question #2 : Exponents

Find the value of x such that:

8x-3 = 164-x

Possible Answers:

7/2

4

11/3

19/4

25/7

Correct answer:

25/7

Explanation:

In order to solve this equation, we first need to find a common base for the exponents. We know that 23 = 8 and 24 = 16, so it makes sense to use 2 as a common base, and then rewrite each side of the equation as a power of 2.

8x-3 = (23)x-3

We need to remember our property of exponents which says that (ab)c = abc.

Thus (23)x-3 = 23(x-3) = 23x - 9.

We can do the same thing with 164-x.

164-x = (24)4-x = 24(4-x) = 216-4x.

So now our equation becomes

23x - 9 = 216-4x

In order to solve this equation, the exponents have to be equal. 

3x - 9 = 16 - 4x

Add 4x to both sides.

7x - 9 = 16

Add 9 to both sides.

7x = 25

Divide by 7.

x = 25/7.

Example Question #1 : Exponents

Which of the following is equal to 410 + 410 + 410 + 410 + 411?

Possible Answers:

250

260

223

215

240

Correct answer:

223

Explanation:

We can start by rewriting 411 as 4 * 410. This will allow us to collect the like terms 410 into a single term.

410 + 410 + 410 + 410 + 411

= 410 + 410 + 410 + 410 + 4 * 410

= 8 * 410

Because the answer choices are written with a base of 2, we need to rewrite 8 and 4 using bases of two. Remember that 8 = 23, and 4 = 22.

8 * 410

= (23)(22)10

We also need to use the property of exponents that (ab)c = abc. We can rewrite (22)10 as 22x10 = 220.

(23)(22)10

= (23)(220)

Finally, we must use the property of exponents that a* ac = ab+c.

(23)(220) = 223

The answer is 223.

Example Question #2 : Exponents

If 3 + 3n+3 = 81, what is 3n+2 ?

Possible Answers:

26

3

9

18

81

Correct answer:

26

Explanation:

3 + 3n+3 = 81

In this equation, there is a common factor of 3, which can be factored out.

Thus, 3(1 + 3n+2) = 81

Note: when 3 is factored out of 3n+3, the result is 3n+2 because (3n+3 = 31 * 3n+2). Remember that exponents are added when common bases are multiplied.  Also remember that 3 = 31.

3(1 + 3n+2) = 81

(1 + 3n+2) = 27

3n+2 = 26

Note: do not solve for n individually.  But rather seek to solve what the problem asks for, namely 3n+2.  

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