ACT Math : ACT Math

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #101 : Algebraic Functions

If f(x)=x^{2}+3\(\displaystyle f(x)=x^{2}+3\), then f(x+h)=\(\displaystyle f(x+h)=\) ?

Possible Answers:

x^{2}+2xh+h^{2}+3\(\displaystyle x^{2}+2xh+h^{2}+3\)

x^{2}+3+h\(\displaystyle x^{2}+3+h\)

x^{2}+2xh+h^{2}\(\displaystyle x^{2}+2xh+h^{2}\)

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

x^{2}+h^{2}+3\(\displaystyle x^{2}+h^{2}+3\)

Correct answer:

x^{2}+2xh+h^{2}+3\(\displaystyle x^{2}+2xh+h^{2}+3\)

Explanation:

To find f(x+h)\(\displaystyle f(x+h)\) when f(x)=x^{2}+3\(\displaystyle f(x)=x^{2}+3\), we substitute (x+h)\(\displaystyle (x+h)\) for x\(\displaystyle x\) in f(x)\(\displaystyle f(x)\).

Thus, f(x+h)=(x+h)^{2}+3\(\displaystyle f(x+h)=(x+h)^{2}+3\).

We expand (x+h)^{2}\(\displaystyle (x+h)^{2}\)  to x^{2}+xh+xh+h^{2}\(\displaystyle x^{2}+xh+xh+h^{2}\).

We can combine like terms to get x^{2}+2xh+h^{2}\(\displaystyle x^{2}+2xh+h^{2}\).

We add 3 to this result to get our final answer.

Example Question #12 : Algebraic Functions

What is the value of the function f(x) = 6x+ 16x – 6 when x = –3?

Possible Answers:

–108

0

–12

96

Correct answer:

0

Explanation:

There are two ways to do this problem. The first way just involves plugging in –3 for x and solving 6〖(–3)〗+ 16(–3) – 6, which equals 54 – 48 – 6 = 0. The second way involves factoring the polynomial to (6x – 2)(x + 3) and then plugging in –3 for x. The second way quickly shows that the answer is 0 due to multiplying by (–3 + 3).

Example Question #11 : Algebraic Functions

Given the functions f(x) = 2x + 4 and g(x) = 3x – 6, what is f(g(x)) when = 6?

Possible Answers:

16

28

192

12

144

Correct answer:

28

Explanation:

We need to work from the inside to the outside, so g(6) = 3(6) – 6 = 12.

Then f(g(6)) = 2(12) + 4 = 28.

Example Question #12 : How To Find F(X)

A function f(x) = –1 for all values of x. Another function g(x) = 3x for all values of x. What is g(f(x)) when x = 4?

Possible Answers:

–1

3

–12

12

–3

Correct answer:

–3

Explanation:

We work from the inside out, so we start with the function f(x). f(4) = –1. Then we plug that value into g(x), so g(f(x)) = 3 * (–1) = –3.

Example Question #342 : Algebra

What is f(–3) if f(x) = x2 + 5?

Possible Answers:

–4

14

4

15

–14

Correct answer:

14

Explanation:

f(–3) = (–3)2 + 5 = 9 + 5 = 14

Example Question #21 : How To Find F(X)

For all values of x, f(x) = 7x2 – 3, and for all values of y, g(y) = 2y + 9. What is g(f(x))?

Possible Answers:

14y2 + 3

7y2 – 3

14x2 – 3

14x2 + 3

2x + 9

Correct answer:

14x2 + 3

Explanation:

The inner function f(x) is like our y-value that we plug into g(y).

g(f(x)) = 2(7x2 – 3) + 9 = 14x2 – 6 + 9 = 14x2 + 3.

Example Question #22 : How To Find F(X)

Find \(\displaystyle f(6)\)

\(\displaystyle f(x)=|x^{2}+4x-127|\)

Possible Answers:

\(\displaystyle 67\)

\(\displaystyle -67\)

\(\displaystyle -136\)

\(\displaystyle -36\)

\(\displaystyle 36\)

Correct answer:

\(\displaystyle 67\)

Explanation:

Simply plug 6 into the equation and don't forget the absolute value at the end.

\(\displaystyle =36+24-127=-67\)

absolute value = 67

Example Question #23 : How To Find F(X)

An outpost has the supplies to last 2 people for 14 days. How many days will the supplies last for 7 people?

Possible Answers:

\dpi{100} \small 4\(\displaystyle \dpi{100} \small 4\)

\dpi{100} \small 9\(\displaystyle \dpi{100} \small 9\)

\dpi{100} \small 10\(\displaystyle \dpi{100} \small 10\)

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

\dpi{100} \small 5\(\displaystyle \dpi{100} \small 5\)

Correct answer:

\dpi{100} \small 4\(\displaystyle \dpi{100} \small 4\)

Explanation:

Supplies are used at the rate of \dpi{100} \small \frac{Supplies}{Days\times People}\(\displaystyle \dpi{100} \small \frac{Supplies}{Days\times People}\).

Since the total amount of supplies is the same in either case, \dpi{100} \small \frac{1}{14\times 2}=\frac{1}{7\times \ (\&hash;\ of\ days)}\(\displaystyle \dpi{100} \small \frac{1}{14\times 2}=\frac{1}{7\times \ (\&hash;\ of\ days)}\).

Solve for days to find that the supplies will last for 4 days.

Example Question #24 : How To Find F(X)

Worker \dpi{100} \small A\(\displaystyle \dpi{100} \small A\) can make a trinket in 4 hours, Worker \dpi{100} \small B\(\displaystyle \dpi{100} \small B\) can make a trinket in 2 hours. When they work together, how long will it take them to make a trinket?

Possible Answers:

\dpi{100} \small \ 1 \frac{1}{3}\ hours\(\displaystyle \dpi{100} \small \ 1 \frac{1}{3}\ hours\)

\dpi{100} \small 6\ hours\(\displaystyle \dpi{100} \small 6\ hours\)

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

\dpi{100} \small \ 1 \frac{1}{2}\ hours\(\displaystyle \dpi{100} \small \ 1 \frac{1}{2}\ hours\)

\dpi{100} \small \frac{1}{2}\ hour\(\displaystyle \dpi{100} \small \frac{1}{2}\ hour\)

Correct answer:

\dpi{100} \small \ 1 \frac{1}{3}\ hours\(\displaystyle \dpi{100} \small \ 1 \frac{1}{3}\ hours\)

Explanation:

The rates are what needs to be added. Rate \dpi{100} \small A\(\displaystyle \dpi{100} \small A\) is \dpi{100} \small \frac{1}{4}\(\displaystyle \dpi{100} \small \frac{1}{4}\), or one trinket every 4 hours. Rate \dpi{100} \small B\(\displaystyle \dpi{100} \small B\) is \dpi{100} \small \frac{1}{2}\(\displaystyle \dpi{100} \small \frac{1}{2}\), one per two hours.

\dpi{100} \small \frac{1}{4}+ \frac{1}{2}=\frac{3}{4}\(\displaystyle \dpi{100} \small \frac{1}{4}+ \frac{1}{2}=\frac{3}{4}\), their combined rate in trinkets per hour.

Now invert the equation to get back to hours per trinket, which is what the question asks for: \dpi{100} \small \frac{4}{3}\ or \ 1 \frac{1}{3}\(\displaystyle \dpi{100} \small \frac{4}{3}\ or \ 1 \frac{1}{3}\)

Example Question #41 : Algebraic Functions

\(\displaystyle a\ \mho \ b = a(b+1)-3\)

 

Quantity A                  Quantity B  

    \(\displaystyle 1\ \mho\ 1\)                           \(\displaystyle 2\ \mho\ 0\)

Possible Answers:

The relationship cannot be determined from the information given.

Quantity A is greater

Quantity B is greater

Quantity A and Quantity B are equal

Correct answer:

Quantity A and Quantity B are equal

Explanation:

Since \(\displaystyle a\ \mho \ b = a(b+1)-3\), then we have that 

\(\displaystyle 1\ \mho \ 1=1(1+1)-3=-1\)

and

\(\displaystyle 2\ \mho \ 0=2(0+1)-3=-1\).

Thus, the two quantities are equal. 

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