PSAT Math : PSAT Mathematics

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #31 : Algebra

Which of these expressions can be simplified further by collecting like terms?

Possible Answers:

\(\displaystyle 12a+12b\)

None of the expressions in the other choices can be simplified further

\(\displaystyle 7b+13b^{2}\)

\(\displaystyle 7ab+13b\)

\(\displaystyle 7ab+12ab^{2}\)

Correct answer:

None of the expressions in the other choices can be simplified further

Explanation:

A binomial can be simplified further if and only if the two terms have the same combination of variables and the same exponents for each like variable. This is not the case in any of the four binomials given, so none of the expressions can be simplified further.

Example Question #691 : Psat Mathematics

Solve for \(\displaystyle x\).

\(\displaystyle \frac{x^{2}+2x-8}{x^{2}+5x-14}=\frac{3}{4}\)

Possible Answers:

\(\displaystyle 11\)

\(\displaystyle 3\)

\(\displaystyle 0\)

\(\displaystyle 5\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle 5\)

Explanation:

\(\displaystyle \frac{x^{2}+2x-8}{x^{2}+5x-14}=\frac{3}{4}\)

Factor the expression

numerator: find two numbers that add to 2 and multiply to -8 [use 4,-2]

denominator: find two numbers that add to 5 and multiply to -14 [use 7,-2]

 

new expression:

\(\displaystyle \frac{(x+4)(x-2)}{(x+7)(x-2)}=\frac{3}{4}\)

Cancel the \(\displaystyle x-2\) and cross multiply.

\(\displaystyle 4(x+4)=3(x+7)\)

\(\displaystyle 4x+16=3x+21\)

\(\displaystyle x=5\)

Example Question #4 : How To Find The Value Of The Coefficient

Give the coefficient of \(\displaystyle x^{2}\) in the product  

\(\displaystyle \left ( 2x + \frac{1}{3}\right ) \left ( x- \frac{1}{6}\right ) \left ( x+ \frac{1}{4}\right )\)

Possible Answers:

\(\displaystyle \frac{11}{12}\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{7}{6}\)

\(\displaystyle \frac{1}{4}\)

\(\displaystyle \frac{1}{6}\)

Correct answer:

\(\displaystyle \frac{1}{2}\)

Explanation:

While this problem can be answered by multiplying the three binomials, it is not necessary. There are three ways to multiply one term from each binomial such that two \(\displaystyle x\) terms and one constant are multiplied; find the three products and add them, as follows:

\(\displaystyle \left ( \underline{2x }+ \frac{1}{3}\right ) \left ( \underline{x}- \frac{1}{6}\right ) \left ( x\underline{+ \frac{1}{4}}\right )\)

\(\displaystyle 2x \cdot x \cdot \frac{1}{4} = \frac{1}{2}x^{2}\)

 

\(\displaystyle \left ( \underline{2x }+ \frac{1}{3}\right ) \left ( x \underline{- \frac{1}{6}}\right ) \left ( \underline{x}+ \frac{1}{4}\right )\)

\(\displaystyle 2x \cdot \left (- \frac{1}{6} \right ) \cdot x = - \frac{1}{3}x^{2}\)

 

\(\displaystyle \left ( 2x\underline{ + \frac{1}{3}}\right ) \left ( \underline{x}- \frac{1}{6}\right ) \left ( \underline{x}+ \frac{1}{4}\right )\)

\(\displaystyle \frac{1}{3} \cdot x \cdot x= \frac{1}{3}x^{2}\)

 

Add: \(\displaystyle \frac{1}{2}x^{2} +\left ( - \frac{1}{3}x^{2} \right ) + \frac{1}{3}x^{2} = \frac{1}{2}x^{2}\)

The correct response is \(\displaystyle \frac{1}{2}\).

Example Question #3 : Binomials

Give the coefficient of \(\displaystyle x^{5}\) in the binomial expansion of \(\displaystyle \left ( 2x+ 0.5\right )^{8}\).

Possible Answers:

\(\displaystyle 224\)

\(\displaystyle 26,880\)

\(\displaystyle 1\)

\(\displaystyle 14\)

\(\displaystyle 1,680\)

Correct answer:

\(\displaystyle 224\)

Explanation:

If the expression \(\displaystyle \left ( A x + B\right )^{n}\) is expanded, then by the binomial theorem, the \(\displaystyle x^{k}\) term is

\(\displaystyle C(n, k) \cdot\left ( Ax \right )^{k} \cdot B ^{n - k}\)

\(\displaystyle = C(n, k) \cdot A ^{k} \cdot B ^{n - k} \cdot x^{k}\)

or, equivalently, the coefficient of \(\displaystyle x^{k}\) is 

\(\displaystyle C(n, k) \cdot A ^{k} \cdot B ^{n - k}\)

Therefore, the \(\displaystyle x^{5}\) coefficient can be determined by setting 

\(\displaystyle A = 2, B =0.5, k=5, n = 8\):

\(\displaystyle C(8,5) \cdot 2^{5} \cdot 0.5 ^{8-5}\)

\(\displaystyle =C(8,5) \cdot 2^{5} \cdot 0.5 ^{3}\)

\(\displaystyle = 56\cdot 32 \cdot 0.125\)

\(\displaystyle =224\)

Example Question #2 : Coefficients

Give the coefficient of \(\displaystyle x^{4}\) in the binomial expansion of \(\displaystyle \left (6x+ \frac{1}{6}\right )^{7}\).

Possible Answers:

\(\displaystyle 5,040\)

\(\displaystyle 1\)

\(\displaystyle 140\)

\(\displaystyle \frac{35}{6}\)

\(\displaystyle 210\)

Correct answer:

\(\displaystyle 210\)

Explanation:

If the expression \(\displaystyle \left ( A x + B\right )^{n}\) is expanded, then by the binomial theorem, the \(\displaystyle x^{k}\) term is

\(\displaystyle C(n, k) \cdot\left ( Ax \right )^{k} \cdot B ^{n - k}\)

\(\displaystyle = C(n, k) \cdot A ^{k} \cdot B ^{n - k} \cdot x^{k}\)

or, equivalently, the coefficient of \(\displaystyle x^{k}\) is 

\(\displaystyle C(n, k) \cdot A ^{k} \cdot B ^{n - k}\)

Therefore, the \(\displaystyle x^{4}\) coefficient can be determined by setting 

\(\displaystyle A = 6, B = \frac{1}{6}, n = 7, k= 4\):

\(\displaystyle C(7,4) \cdot 6 ^{4} \cdot\left ( \frac{1}{6} \right ) ^{7-4}\)

\(\displaystyle =C(7,4) \cdot 6 ^{4} \cdot\left ( \frac{1}{6} \right ) ^{3}\)

\(\displaystyle =35 \cdot 1,296 \cdot \frac{1}{216}\)

\(\displaystyle = 210\)

Example Question #1 : How To Find The Value Of The Coefficient

Give the coefficient of \(\displaystyle x^{5}\) in the binomial expansion of \(\displaystyle \left ( 0.2x+ 5 \right )^{7}\).

Possible Answers:

\(\displaystyle 20.16\)

\(\displaystyle 0.168\)

\(\displaystyle 315,000\)

\(\displaystyle 2,625\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 0.168\)

Explanation:

If the expression \(\displaystyle \left ( A x + B\right )^{n}\) is expanded, then by the binomial theorem, the \(\displaystyle x^{k}\) term is

\(\displaystyle C(n, k) \cdot\left ( Ax \right )^{k} \cdot B ^{n - k}\)

\(\displaystyle = C(n, k) \cdot A ^{k} \cdot B ^{n - k} \cdot x^{k}\)

or, equivalently, the coefficient of \(\displaystyle x^{k}\) is 

\(\displaystyle C(n, k) \cdot A ^{k} \cdot B ^{n - k}\)

Therefore, the \(\displaystyle x^{5}\) coefficient can be determined by setting 

\(\displaystyle A = 0.2, B =5, k=5, n = 7\)

\(\displaystyle C(7,5) \cdot 0.2^{5} \cdot 5 ^{7 - 5}\)

\(\displaystyle = C(7,5) \cdot 0.2 ^{5} \cdot 5 ^{2}\)

\(\displaystyle = 21\cdot 0.00032 \cdot 25\)

\(\displaystyle = 0.168\)

Example Question #5 : Binomials

Give the coefficient of \(\displaystyle x^{2}\) in the product

\(\displaystyle \left (3x- 7 \right ) \left ( 4x+3\right )\left ( 2x-7\right )\).

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle -122\)

\(\displaystyle 75\)

\(\displaystyle 158\)

\(\displaystyle 46\)

Correct answer:

\(\displaystyle -122\)

Explanation:

While this problem can be answered by multiplying the three binomials, it is not necessary. There are three ways to multiply one term from each binomial such that two \(\displaystyle x\) terms and one constant are multiplied; find the three products and add them, as follows:

\(\displaystyle \left (\underline{3x}- 7 \right ) \left ( \underline{4x}+3\right )\left ( 2x\underline{-7}\right )\)

\(\displaystyle 3x \cdot 4x \cdot (-7) = -84x^{2}\)

 

\(\displaystyle \left (\underline{3x}- 7 \right ) \left ( 4x\underline{+3}\right )\left ( \underline{2x}-7\right )\)

\(\displaystyle 3x \cdot 3 \cdot 2x = 18x^{2}\)

 

\(\displaystyle \left (3x\underline{- 7} \right ) \left ( \underline{4x}+3\right )\left ( \underline{2x}-7\right )\)

\(\displaystyle -7 \cdot 4x \cdot 2x = -56x^{2}\)

 

Add: \(\displaystyle -84x^{2} + 18x^{2} - 56x^{2} = -122x^{2}\)

The correct response is -122.

Example Question #2 : Coefficients

Give the coefficient of \(\displaystyle x^{2}\) in the product  

\(\displaystyle \left ( x+ 0.4\right ) (x - 0.2) (3x-0.7)\).

Possible Answers:

\(\displaystyle -0.1\)

\(\displaystyle 0.5\)

\(\displaystyle 1.3\)

\(\displaystyle 2.5\)

\(\displaystyle 0.7\)

Correct answer:

\(\displaystyle -0.1\)

Explanation:

While this problem can be answered by multiplying the three binomials, it is not necessary. There are three ways to multiply one term from each binomial such that two \(\displaystyle x\) terms and one constant are multiplied; find the three products and add them, as follows:

 

\(\displaystyle \left (\underline{ x}+ 0.4\right ) (\underline{x} - 0.2) (3x\underline{-0.7})\)

\(\displaystyle x \cdot x \cdot (-0.7) = -0.7x^{2}\)

 

\(\displaystyle \left (\underline{ x}+ 0.4\right ) (x \underline{-0.2})(\underline{3x}-0.7)\)

\(\displaystyle x \cdot (-0.2) \cdot 3x= -0.6x^{2}\)

 

\(\displaystyle \left (x+ \underline{0.4}\right ) (\underline{x} - 0.2)(\underline{3x}-0.7)\)

\(\displaystyle 0.4 \cdot x \cdot 3x = 1.2 x^{2}\)

 

Add: \(\displaystyle -0.7x^{2}+ (-0.6x^{2})+ 1.2x^{2} = -0.1x^{2}\).

The correct response is \(\displaystyle -0.1\).

Example Question #21 : Polynomials

Multiply the binomial.

\(\displaystyle (x-3)(x+4)\)

Possible Answers:

\(\displaystyle x^{2}+x-12\)

\(\displaystyle x^{2}-x-12\)

\(\displaystyle x^{2}-12\)

\(\displaystyle x^{2}+x+12\)

Correct answer:

\(\displaystyle x^{2}+x-12\)

Explanation:

By multiplying with the foil method, we multiply our first values giving \(\displaystyle x^2\), our outside values giving \(\displaystyle 4x\). our inside values which gives \(\displaystyle -3x\), and out last values giving \(\displaystyle -12\).

Example Question #1 : How To Factor A Trinomial

Factor the following expression completely:

\(\displaystyle x^4-8x^3+12x^2\)

Possible Answers:

\(\displaystyle x^2(x-3)(x-4)\)

\(\displaystyle x^2(x-6)(x-2)\)

\(\displaystyle x^2(x+6)(x+2)\)

\(\displaystyle x^2(x^2-8x+12)\)

\(\displaystyle x^2(x+3)(x+4)\)

Correct answer:

\(\displaystyle x^2(x-6)(x-2)\)

Explanation:

We must begin by factoring out \(\displaystyle x^2\) from each term.

\(\displaystyle x^2(x^2-8x+12)\)

Next, we must find two numbers that sum to \(\displaystyle -8\) and multiply to \(\displaystyle 12\).

\(\displaystyle (-6)+(-2)=-8\)

\(\displaystyle -6*-2=12\)

Thus, our final answer is:

\(\displaystyle x^2(x-6)(x-2)\)

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