ISEE Lower Level Math : How to find the solution to an equation

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

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Example Questions

Example Question #111 : Algebraic Concepts

\displaystyle 6x =15

Possible Answers:

\displaystyle x = .4

\displaystyle x = 2.6

\displaystyle x = 2.4

\displaystyle x = 2.5

Correct answer:

\displaystyle x = 2.5

Explanation:

To solve for \displaystyle x in the equation

 \displaystyle 6x = 15

Divide both sides by the coefficient of \displaystyle x, which is \displaystyle 6.

\displaystyle \frac{6x}{6} = \frac{15}{6}

\displaystyle x = 2\frac{1}{2}

Convert fraction to decimal:

\displaystyle x = 2.5

Example Question #112 : Algebraic Concepts

\displaystyle \frac{23}{x} = 5

Possible Answers:

\displaystyle x =4.4

\displaystyle x= 4.5

\displaystyle x = 4.3

\displaystyle x = 4.6

Correct answer:

\displaystyle x = 4.6

Explanation:

To solve 

\displaystyle \frac{23}{x} = 5 

\displaystyle \frac{x}{1} (\frac{23}{x}) = \frac{x}{1} (\frac{5}{1})

\displaystyle 23 = 5x

\displaystyle \frac{23}{5} = x

\displaystyle 4\frac{3}{5} = x

Convert to equivalent fraction with \displaystyle 10 as the denominator.

\displaystyle 4\frac{3}{5} = 4\frac{6}{10}

Convert to a decimal

\displaystyle 4\frac{6}{10} = 4.6

\displaystyle x = 4.6 is the correct answer.

 

Example Question #113 : Algebraic Concepts

If \displaystyle 7x + 3 = 17 and \displaystyle 2y - 9 = -15, then what is the product of\displaystyle (x)(y)?

Possible Answers:

\displaystyle -24

\displaystyle 6

\displaystyle -6

\displaystyle 24

Correct answer:

\displaystyle -6

Explanation:

To determine the product of \displaystyle (x)(y), first solve each equation to get the values of those variables.

\displaystyle 7x + 3 = 17

Subtract \displaystyle 3 from both sides of the equation:

\displaystyle 7x + 3 - 3 = 17-3

\displaystyle 7x = 14

Divide both sides by the coefficient, which is\displaystyle 7.

\displaystyle \frac{7x}{7} =\frac{14}{7}

\displaystyle x = 2

 

\displaystyle 2y-9 = -15

Add \displaystyle 9 to both sides of the equation:

\displaystyle 2y - 9 + 9 = -15 + 9

\displaystyle 2y = -6

Divide both sides of the equation by the coefficient of the variable\displaystyle y, which is 2

\displaystyle \frac{2y}{2} = \frac{-6}{2}

\displaystyle y = -3

If \displaystyle x = 2 and  \displaystyle y = -3

 then the product of \displaystyle (2) (-3) = -6

\displaystyle -6 is the correct answer.

Example Question #113 : Algebraic Concepts

If \displaystyle y = 3, which of the following number sentences is true?

Possible Answers:

\displaystyle 6y + 4 = 18

\displaystyle 4 (y+7) = 40

\displaystyle 2 (y-2) = 6

\displaystyle 5y = 9

Correct answer:

\displaystyle 4 (y+7) = 40

Explanation:

In order to find the solution, simply place the value of \displaystyle y, which is \displaystyle 3, in each equation.

\displaystyle (6) (3) + 4 \neq 18 

\displaystyle 2(3-2) \neq 6

\displaystyle 5 (3) - 9 \neq -6

The only equation that is a true numerical statement if \displaystyle y = 3 is

\displaystyle 4 (3+7) = 40

Example Question #114 : Algebraic Concepts

Jaden has \displaystyle \$22 in his piggy bank. What algebraic expressions would be used to determine how much Jaden needs to buy a video game that costs \displaystyle \$56?

Possible Answers:

\displaystyle \$22 x = \$56

\displaystyle \$56 + \$22 = x

\displaystyle 22 \times 56 = x

\displaystyle \$22 + x = \$56

Correct answer:

\displaystyle \$22 + x = \$56

Explanation:

Jaden already has \displaystyle \$22 of the \displaystyle \$56. The variable would need to represent how much would be added to \displaystyle $22 to reach his goal of \displaystyle $56.   

Therefore, 

\displaystyle \$22 + x = \$56 is the equation that you would use to solve this word problem.

Example Question #115 : Algebraic Concepts

Solve when \displaystyle x = -2

\displaystyle 2x^{3} -3x +7

Possible Answers:

\displaystyle -3

\displaystyle 3

\displaystyle -11

\displaystyle 11

Correct answer:

\displaystyle -3

Explanation:

To solve, insert \displaystyle -2 for each \displaystyle x variable in the equation.

\displaystyle 2(-2^{3}) - 3(-2) + 7 =

Using the Order of Operations, PEMDAS, solve the equation. PEMDAS stands for parentheses, exponents, multiplication/division, addition/subtraction. Remember the exponent tells you how many times to multiply the number by itself.

\displaystyle -2^{3} = (-2) (-2) (-2) = -8

The subtraction of a negative is the same as adding a positive.

\displaystyle 2(-8) +6 + 7 =

\displaystyle -16 + 13 = -3

 

Example Question #116 : Algebraic Concepts

What is the value of \displaystyle x in the following equation?

\displaystyle 4 (x-3) = -23 + (3\times 5)

Possible Answers:

\displaystyle x = -2

\displaystyle x = 2

\displaystyle x = -1

\displaystyle x = 1

Correct answer:

\displaystyle x = 1

Explanation:

To solve:

\displaystyle 4 (x-3) = -23 + (3\times 5)

First distribute the \displaystyle 4 to the terms inside the parentheses, and then solve using the Order of Operations or PEMDAS (Parentheses, Exponents. Multiplication/Division, Addition/Subtraction):

\displaystyle 4x-12 = -23 + 15 

\displaystyle 4x -12 = -8

\displaystyle 4x -12 + 12 = -8 + 12

\displaystyle 4x = 4

\displaystyle \frac{4x}{4} = \frac{4}{4}

\displaystyle x = 1 is the correct answer.

Example Question #117 : Algebraic Concepts

If \displaystyle \small y=5, which of the following number sentences are true?

Possible Answers:

\displaystyle \small 3y-6=19

\displaystyle \small 2\left ( y-2\right )=6

\displaystyle \small 4y+7=20

\displaystyle \small 5\left ( y+4\right )=42

Correct answer:

\displaystyle \small 2\left ( y-2\right )=6

Explanation:

Replace the variable \displaystyle \small y with \displaystyle \small 5. Then solve using order of operation (PEMDAS).

\displaystyle \small 2\left ( y-2\right )=6

\displaystyle \small 2\left ( 5-2\right )=6

\displaystyle \small 5-2=3

\displaystyle \small 2\times3=6

Example Question #118 : Algebraic Concepts

Solve for x in the following equation:

\displaystyle 2x = 40

Possible Answers:

\displaystyle x = 15

\displaystyle x = 42

\displaystyle x = 20

\displaystyle x = 38

\displaystyle x = 40

Correct answer:

\displaystyle x = 20

Explanation:

To solve for in this equation, we must get x to stand alone or get x by itself.  

In the equation

\displaystyle 2x = 40

to get x by itself, we must cancel out the 2 next to it.  To cancel it out, we will divide by 2.  If we divide on the left side, we must divide on the right.  So,

\displaystyle \frac{2x}{2} = \frac{40}{2}

\displaystyle x = 20

Therefore, after getting x to stand alone, we can see that \displaystyle x=20.

Example Question #119 : Algebraic Concepts

Solve for a in the following equation:

\displaystyle a - 5 = 2

Possible Answers:

\displaystyle a=5

\displaystyle a=2

\displaystyle a=25

\displaystyle a=7

\displaystyle a=3

Correct answer:

\displaystyle a=7

Explanation:

To solve for a, we want to get a to stand alone or be by itself.  To do that, in the equation

\displaystyle a-5=2

we need to cancel out the 5.  In this case, we are subtracting 5 on the left side.  To cancel it out, we need to add 5.  If we add 5 to the left side, we need to add 5 to the right side.  So we get

\displaystyle a-5+5=2+5

\displaystyle a+0 = 7

\displaystyle a=7

 

Therefore, if we solve for a in the equation, we get \displaystyle a=7.

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