ACT Math : Algebra

Study concepts, example questions & explanations for ACT Math

varsity tutors app store varsity tutors android store varsity tutors ibooks store

Example Questions

Example Question #1842 : Sat Mathematics

If x= 8, then x2(4/(3 – x))(2/(4 – x)) – (4/x2) = ?

Possible Answers:

22

15

35

0

16

Correct answer:

15

Explanation:

There is really no need to alter this equation using algebra. Simply find that x = 2 and plug in. We see that 4(4)(1) – (1)=15. Remember to use correct order of operations here (parentheses, exponents, multiplication, division, addition, subtraction).

Example Question #351 : Algebra

Find the intersection of the following two equations:

3x + 4y = 6

15x - 4y = 3

Possible Answers:

(1, 0.5)

(0.2, 0)

(0.5, 1.125)

(3, 4)

(18, 0)

Correct answer:

(0.5, 1.125)

Explanation:

The point of intersection for two lines is the same as the values of x and y that mutually solve each equation.  Although you could solve for one variable and replace it in the other equation, use elementary row operations to add the two equations since you have a 4y and -4y:

3x + 4y = 6

15x - 4y = 3

18x = 9; x = 0.5

You can now plug x into the first equation:

3 * 0.5 + 4y = 6; 1.5 +4y = 6; 4y = 4.5; y = 1.125

Therefore, our point of intersection is (0.5, 1.125)

Example Question #352 : Algebra

Two cars start 25 mile apart and drive away from each other in opposite directions at speeds of 50 and 70 miles per hour.  In approximately how many minutes will they be 400 miles apart?

Possible Answers:

3.33

187.5

200

3.125

None of the other answers

Correct answer:

187.5

Explanation:

The cars have a distance from each other of 25 + 120t miles, where t is the number of hours, 25 is their initial distance and 120 is 50 + 70, or their combined speeds.  Solve this equation for 400:

25 + 120t = 400; 120t = 375; t = 3.125

However, the question asked for minutes, so we must multiply this by 60:

3.125 * 60 = 187.5 minutes.

Example Question #353 : Algebra

A given university has an average professor pay of $40,000 a year and an average administrator pay of $45,000 per year. If the ratio of professors to administrators is 4 to 3, and the total pay for professors and administrators in a year is $40,415,000, how many professors does the college have?

Possible Answers:

475

548

411

500

375

Correct answer:

548

Explanation:

Set up a system of linear equations based on our data:

40,000P + 45,000A = 40,415,000

P/A = 4/3

To make things easiest, solve the second equation for A in terms of P:

A = (3/4) P

Replace this value into the first equation:

40,000P + 45,000 * (3/4)P = 40,415,000

Simplify:

40,000P + 33,750P = 40,415,000

73,750P = 40,415,000

P = 548 (The number of professors)

Example Question #65 : How To Find The Solution To An Equation

Abby works at a car dealership and receives a commission "c" which is a percent of the profit the dealership makes from the sale, which is the difference between the price "p" of the car and the value "v" of the car. How much, in dollars, does the dealership earn per transaction?

Possible Answers:

(p – v)(0.01c)

pv(0.01c)

(p – v)(1 – 0.01c)

(p – v)(1 – c)

p(v – 0.01c)

Correct answer:

(p – v)(1 – 0.01c)

Explanation:

To show that c is of the profit of the transaction, we must represent the profit as the difference between the price and the value of the car, or "(p – v)"

To show that Abby's commission in dollars is a percentage of the profit, we use 0.01 * c to convert the commission she earns to a percent.

To shift the earnings from Abby to the dealership (which is what the question requires of us), we must take 1 – 0.01c since this will accommodate for the remaining percentage. For example, it shifts 75% (0.75) to 25% (1 – 0.75 or 0.25).

Putting this all together, we get a final expression of:

(p – v)(1 – 0.01c) = dealership earnings

Check answer with arbitrary values: letting p = 300, v = 200, and c = 20, we get a value of 80 which makes sense as the $100 profit must be distributed evenly between Abby ($20) and the dealership ($80).

Example Question #43 : Linear / Rational / Variable Equations

A theme park charges $10 for adults and $5 for kids. How many kids tickets were sold if a total of 548 tickets were sold for a total of $3750?

Possible Answers:

346

431

269

248

157

Correct answer:

346

Explanation:

Let c = number of kids tickets sold. Then (548 – c) adult tickets were sold. The revenue from kids tickets is $5c, and the total revenue from adult tickets is $10(548 – c). Then,

5c + 10(548 – c) = 3750

5c + 5480 – 10c = 3750

5c = 1730

c = 346. 

We can check to make sure that this number is correct:

$5 * 346 tickets + $10 * (548 – 346) tickets = $3750 total revenue

Example Question #72 : Algebra

Two palm trees grow next to each other in Luke's backyard. One of the trees gets sick, so Luke cuts off the top 3 feet. The other tree, however, is healthy and grows 2 feet. How tall are the two trees if the healthy tree is now 4 feet taller than the sick tree, and together they are 28 feet tall?

Possible Answers:

cannot be determined

11 and 17 feet

8 and 20 feet

12 and 16 feet

14 and 14 feet

Correct answer:

12 and 16 feet

Explanation:

Let s stand for the sick tree and h for the healthy tree. The beginning information about cutting the sick tree and the healthy tree growing is actually not needed to solve this problem! We know that the healthy tree is 4 feet taller than the sick tree, so h = s + 4.

We also know that the two trees are 28 feet tall together, so s + h = 28. Now we can solve for the two tree heights.

Plug h = s + 4 into the second equation: (s + 4) + s = 28. Simplify and solve for h: 2s = 24 so s = 12. Then solve for h: h = s + 4 = 12 + 4 = 16.

Example Question #44 : Linear / Rational / Variable Equations

Solve for z

3(z + 4)3 – 7 = 17

Possible Answers:

8

2

–2

4

–8

Correct answer:

–2

Explanation:

1. Add 7 to both sides

3(z + 4)3 – 7 + 7= 17 + 7

3(z + 4)3 = 24

2. Divide both sides by 3

(z + 4)3 = 8

3. Take the cube root of both sides

z + 4 = 2

4. Subtract 4 from both sides

z = –2

Example Question #45 : Linear / Rational / Variable Equations

Jen and Karen are travelling for the weekend. They both leave from Jen's house and meet at their destination 250 miles away. Jen drives 45mph the whole way. Karen drives 60mph but leaves a half hour after Jen. How long does it take for Karen to catch up with Jen? 

Possible Answers:

\dpi{100} \small 1 \ hour

She can't catch up. 

\dpi{100} \small 1.5 \ hours

\dpi{100} \small 3 \ hours

\dpi{100} \small 2 \ hours

Correct answer:

\dpi{100} \small 1.5 \ hours

Explanation:

For this type of problem, we use the formula:

\dpi{100} \small distance = rate\times time

When Karen catches up with Jen, their distances are equivalent. Thus,

\dpi{100} \small rate (Jen) \times time (Jen)=rate(Karen)\times time(Karen)

We then make a variable for Jen's time, \dpi{100} \small t. Thus we know that Karen's time is \dpi{100} \small t-.5 (since we are working in hours).

Thus,

 

There's a logical shortcut you can use on "catching up" distance/rate problems. The difference between the faster (Karen at 60mph) and slower (Jen at 45mph) drivers is 15mph.  Which means that every one hour, the faster driver, Karen, gains 15 miles on Jen.  We know that Jen gets a 1/2 hour head start, which at 45mph means that she's 22.5 miles ahead when Karen gets started.  So we can calculate the number of hours (H) of the 15mph of Karen's "catchup speed" (the difference between their speeds) it will take to make up the 22.5 mile gap:

15H = 22.5

So H = 1.5.

Example Question #46 : Linear / Rational / Variable Equations

Bill and Bob are working to build toys. Bill can build \dpi{100} \small k toys in 6 hours. Bob can build \dpi{100} \small k toys in 3 hours. How long would it take Bob and Bill to build \dpi{100} \small 4k toys working together? 

Possible Answers:

\dpi{100} \small 12\ hours

\dpi{100} \small 2\ hours

\dpi{100} \small 9\ hours

\dpi{100} \small 4\ hours

\dpi{100} \small 8\ hours

Correct answer:

\dpi{100} \small 8\ hours

Explanation:

Bill builds \dpi{100} \small \frac{k}{6} toys an hour. Bob builds \dpi{100} \small \frac{k}{3} toys an hour. Together, their rate of building is \dpi{100} \small \frac{k}{6}+\frac{k}{3}=\frac{k}{2}. Together they can build \dpi{100} \small k toys in 2 hours. They would be able to build \dpi{100} \small 4k toys in 8 hours. 

Learning Tools by Varsity Tutors