ISEE Upper Level Math : How to multiply variables

Study concepts, example questions & explanations for ISEE Upper Level Math

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Example Questions

Example Question #11 : How To Multiply Variables

Simplify:
\(\displaystyle (-\frac{5}{3})^{-3}\)
Possible Answers:

\(\displaystyle -\frac{125}{27}\)

\(\displaystyle \frac{125}{27}\)

\(\displaystyle -\frac{27}{125}\)

\(\displaystyle \frac{27}{125}\)

\(\displaystyle -\frac{25}{9}\)

Correct answer:

\(\displaystyle -\frac{27}{125}\)

Explanation:

First, recognize that raising the fraction to a negative power is the same as raising the inverted fraction to a positive power.

\(\displaystyle (-\frac{5}{3})^{-3}=(-\frac{3}{5})^3\)

Apply the exponent within the parentheses and simplify. The negative in the fraction can be applied to either the numerator or the denominator, but not both; we will apply it to the numerator.

\(\displaystyle \frac{(-3)^3}{(5)^3}\)

\(\displaystyle \frac{-27}{125}=-\frac{27}{125}\)

The fraction cannot be simplified further.

Example Question #11 : How To Multiply Variables

Solve for \dpi{100} x\(\displaystyle \dpi{100} x\):

\dpi{100} \frac{1}{3}x-14=7\(\displaystyle \dpi{100} \frac{1}{3}x-14=7\)

Possible Answers:

\dpi{100} 7\(\displaystyle \dpi{100} 7\)

\dpi{100} 3\(\displaystyle \dpi{100} 3\)

\dpi{100} 21\(\displaystyle \dpi{100} 21\)

\dpi{100} 63\(\displaystyle \dpi{100} 63\)

Correct answer:

\dpi{100} 63\(\displaystyle \dpi{100} 63\)

Explanation:

\dpi{100} \frac{1}{3}x-14=7\(\displaystyle \dpi{100} \frac{1}{3}x-14=7\)

\dpi{100} \frac{1}{3}x-14+14=7+14\(\displaystyle \dpi{100} \frac{1}{3}x-14+14=7+14\)

\dpi{100} \frac{1}{3}x=21\(\displaystyle \dpi{100} \frac{1}{3}x=21\)

\dpi{100} 3\cdot \frac{1}{3}x=21\cdot 3\(\displaystyle \dpi{100} 3\cdot \frac{1}{3}x=21\cdot 3\)

\dpi{100} x=63\(\displaystyle \dpi{100} x=63\)

Example Question #11 : Operations

If the product of three consecutive numbers is 990, what is the smallest number?

Possible Answers:

\(\displaystyle 7\)

\(\displaystyle 10\)

\(\displaystyle 9\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 9\)

Explanation:

If the product of three consecutive numbers is 990, then the smallest number can be found by plugging in each answer choice into the scenario to see whether it is correct. 

If we plug in 9 as the smallest number, then the two consecutive numbers would be 10 and 11. 

Given that 9 times 10 times 11 equals 990, that is the correct answer. 

Example Question #903 : Isee Upper Level (Grades 9 12) Mathematics Achievement

What is the simplified version of the expression below?

\(\displaystyle (\frac{5}{4}\cdot8+6\div3)^{2}-12\)

 

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 132\)

\(\displaystyle 24\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 132\)

Explanation:

The first step is to simplify the values in the parentheses:

\(\displaystyle (\frac{5}{4}\cdot8+6\div3)^{2}-12\)

\(\displaystyle (10+2)^{2}-12\)

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

\(\displaystyle 144-12\)

\(\displaystyle 132\)

Example Question #904 : Isee Upper Level (Grades 9 12) Mathematics Achievement

Simplify:
\(\displaystyle 4xy^2-2xy+y^{2}x+y^3-8xy+4yx\)
Possible Answers:

\(\displaystyle 4xy^2-6xy+y^3\)

\(\displaystyle 5xy^2-6xy+y^3\)

\(\displaystyle 4xy^2-10xy+y^3\)

\(\displaystyle xy^2-4xy+y^3\)

\(\displaystyle 4xy^2-10xy+yx^2+y^3+4yx\)

Correct answer:

\(\displaystyle 5xy^2-6xy+y^3\)

Explanation:

Reorder the expression to group like-terms together.

\(\displaystyle 4xy^2-2xy+y^{2}x+y^3-8xy+4yx\)
\(\displaystyle (4xy^2+y^{2}x)+(-2xy+-8xy+4yx)+y^3\)
Simplify by combining like-terms.
\(\displaystyle 5xy^2+(-6xy)+y^3\)
\(\displaystyle 5xy^2-6xy+y^3\)

Example Question #905 : Isee Upper Level (Grades 9 12) Mathematics Achievement

If \(\displaystyle x^{2}-12x\) is a positive number, what is a possible value of \(\displaystyle x\)?

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 8\)

\(\displaystyle -4\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle -4\)

Explanation:

If x is equal to \(\displaystyle -4\), then the equation could be written as follows:

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

\(\displaystyle -4^{2}-(12*-4)\)

\(\displaystyle 16+48=64\)

Given that \(\displaystyle 64\) is a positive number, \(\displaystyle -4\) is a possible value of \(\displaystyle x\)

Example Question #12 : How To Multiply Variables

Megan teaches a cooking class. Every time a student takes a class, the student receives a 10% discount off of the price he paid for the previous class. The first class that Jose took cost $50. What will be the first class in which Jose pays less than $38?

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle 2\)

\(\displaystyle 4\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 4\)

Explanation:

In order to solve this problem, the price of $50 must be discounted by 10% until we get to a price of $38 or less. 

The first class is 50. 

The second class, being 10 percent less than the previous one, is \(\displaystyle 50-.1\cdot 50=50-5=45\)

The third class, being 10 percent less than the previous one, is \(\displaystyle 45-.1\cdot45=45-4.5 = 40.5\)

The fourth class, being 10 percent less than the previous one, is \(\displaystyle 40.5-.1\cdot40.5=40.5-4.05=36.45\)

Therefore, the answer is 4. 

Example Question #907 : Isee Upper Level (Grades 9 12) Mathematics Achievement

Simplify the following expression

\(\displaystyle (6x^2)*(3x^3)\)

Possible Answers:

\(\displaystyle 18x^6\)

\(\displaystyle 9x^6\)

\(\displaystyle 9x^5\)

\(\displaystyle 18x^5\)

Correct answer:

\(\displaystyle 18x^5\)

Explanation:

Simplify the following expression

\(\displaystyle (6x^2)*(3x^3)\)

Let's begin by multiplying our coefficients:

\(\displaystyle 6*3=18\)

Next, we need to realize that we can combine our x's by adding the exponents.

\(\displaystyle x^2*x^3=x^{3+2}=x^5\)

Put it all together to get:

\(\displaystyle 18x^5\)

Example Question #908 : Isee Upper Level (Grades 9 12) Mathematics Achievement

Simplify the following:

\(\displaystyle (9q^3n^3)(q^5n^6)\)

Possible Answers:

\(\displaystyle 81q^8n^9\)

\(\displaystyle 9q^8n^9\)

\(\displaystyle 9q^9n^8\)

\(\displaystyle 9qn^{72}\)

Correct answer:

\(\displaystyle 9q^8n^9\)

Explanation:

Simplify the following:

\(\displaystyle (9q^3n^3)(q^5n^6)\)

To begin, our coefficient will not change. We have just one integer (the 9) and nothing to multiply it by.

To combine our exponents, we will add them. This is because we are multiplying them

\(\displaystyle q^3*q^5=q^{3+5}=q^8\)

\(\displaystyle n^3*n^6=n^{3+6}=n^9\)

Put it together to get:

\(\displaystyle 9q^8n^9\)

Example Question #12 : Operations

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

\(\displaystyle y^{2} = 2\)

\(\displaystyle x\) and \(\displaystyle y\) are both positive.

Evaluate \(\displaystyle (2x+ 3y) (3x-2y)\).

Possible Answers:

\(\displaystyle 66\)

\(\displaystyle 126\)

\(\displaystyle 150\)

\(\displaystyle 90\)

Correct answer:

\(\displaystyle 126\)

Explanation:

Multiply the binomials using the FOIL method - first, outer, inner, last - then combine like terms:

\(\displaystyle (2x+ 3y) (3x-2y)\)

\(\displaystyle = 2x \cdot 3x - 2x \cdot 2y+ 3y \cdot 3x-3y \cdot 2y\)

\(\displaystyle =6 x ^{2}-4 x y+ 9xy-6y^{2}\)

\(\displaystyle =6 x ^{2}+ 5 xy-6y^{2}\)

\(\displaystyle x^{2} = 18\) and \(\displaystyle y^{2} = 2\); also, by the Power of a Product Principle:

\(\displaystyle (xy) ^{2} = x^{2}y^{2}\).

\(\displaystyle x\) and \(\displaystyle y\) are both positive, so, substituting:

\(\displaystyle xy = \sqrt{x^{2}y^{2}} = \sqrt{18 \cdot 2} = \sqrt{36} = 6\).

Again, using substitution:

\(\displaystyle (2x+ 3y) (3x-2y)\)

\(\displaystyle =6 x ^{2}+ 5 xy-6y^{2}\)

\(\displaystyle =6 (18)+ 5 (6)-6 (2)\)

\(\displaystyle =108 +30-12\)

\(\displaystyle =126\)

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