SAT Math : Proportion / Ratio / Rate

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #48 : Proportion / Ratio / Rate

Laura owns a large property. Her lawn is rectangular. It is 500 meters long, and 350 meters wide. If Laura mows the lawn at a rate of 20,000 meters squared per hour, how many hours will it take Laura to finish mowing the lawn?

Possible Answers:

Correct answer:

Explanation:

The area of a rectangle is the length , multiplied by the width . Here the area of the lawn in meters squared is:

 

We found that Laura is mowing 175,000 meters squared at a rate of 20,000 meters squared per hour. 

Plugging in 20,000 for the rate, and 175,000 for the total area gives:

Multiply both sides by the total number of hours:

Now, divide both sides by 20,000: 

 

Example Question #21 : How To Find Rate

Jess is trying to fill her 10,000 gallon pool with water before the summer. She has three hoses, one that pump water at a rate of 175 gallons per hour, 25 gallons per hour and 200 gallons per hour. If she used all three hoses how many hours would it take to fill her pool? 

Possible Answers:

Correct answer:

Explanation:

First add up all of the rates to get the total rate of water flowing into the pool at one time. 

Then to determine the time it takes to fill the pool divide the total volume of the pool by this rate. 

This answer of 25 hours. 

Example Question #22 : How To Find Rate

Joaquin can clean a pool in j minutes.  River can clean the same size pool in r minutes.  Which of the following expresses the time needed for three pools (all of the same size) to be cleaned when Joaquin and River work together?

Possible Answers:

Correct answer:

Explanation:

This is a rate question, so first we should rewrite the "times" given to us as rates.

Joaquin's rate :

 

River's rate:

Now we add their rates together, to find the rate when they work together:

Using the equiation for distance, d = rate * time we can rearrange it to see that to find time we need to do t = distance/rate

in this case, the distance is "3 pools" and the rate is "(j+r)/jr pools per minute".  So we reach our answer:

Example Question #51 : Proportion / Ratio / Rate

If Kara drives a distance of miles every hours, how many hours will it take her to drive a distance of miles, in terms of m, h, and d ?

Possible Answers:

mhd

hmd

dmh

dhm

dhm

Correct answer:

dhm

Explanation:

We need to convert miles into hours. We do so by multiplying d miles by the conversion ratio of miles to hours given in the problem, ( hours / miles), as follows:

miles * ( hours / miles) = (dh )/m  hours.

From this conversion of miles into hours, we see that the number of hours it takes Kara to drive a distance of miles is (dh )/m.

Example Question #72 : Fractions

A TV show lasts 30 minutes, what fraction of the show is left after 12 minutes have passed?

Possible Answers:

12/15

1/3

4/10

2/3

3/5

Correct answer:

3/5

Explanation:

After watching 12 minutes of the show 18 remain. 18 is 60% of the total 30 minutes. As a fraction it can be expressed as 3/5. 

Example Question #1 : How To Find The Ratio Of A Fraction

A bag contains red, orange, and yellow marbles only. The marbles occur in a ratio of 5 red marbles: 4 orange marbles: 1 yellow marble. If one-third of the red marbles, one-half of the orange marbles, and one-fourth of the yellow marbles are removed, then what fraction of the remaining marbles in the bag is red?

Possible Answers:

43/75

39/73

40/73

40/43

37/77

Correct answer:

40/73

Explanation:

Marble_remove1

Marbles_remove2

Example Question #2 : How To Find The Ratio Of A Fraction

Marty drove 40 mi/hr for 3 hours, then 60 mi/hr for 1 hour, and finally 70 mi/hr for the last 2 hours. What was Marty's average speed?

Possible Answers:

47 mi/hr

58 mi/hr

63 mi/hr

60 mi/hr

53 mi/hr

Correct answer:

53 mi/hr

Explanation:

Marty's total driving time was 3 + 1 + 2 = 6 hours. He drove 40 mi/hr for 3 hours, or 3/6 = 1/2 of the time. He drove 60 mi/hr for 1 hour, or 1/6 of the drive. Lastly, he drove 70 mi/hr for 2 hours, or 2/6 = 1/3 of the drive.

To find the average speed, we need to multiply the speeds with their corresponding weights and add them up.

Average = 1/2 * 40 + 1/6 * 60 + 1/3 * 70 = 53.33... ≈ 53 mi/hr

Example Question #2 : How To Find The Ratio Of A Fraction

A pie is made up of   crust,  apples, and  sugar, and the rest is jelly. What is the ratio of crust to jelly?

Possible Answers:

Correct answer:

Explanation:

A pie is made up of   crust,  apples,  sugar, and the rest is jelly. What is the ratio of crust to jelly?

To compute this ratio, you must first ascertain how much of the pie is jelly. This is:

Begin by using the common denominator :

So, the ratio of crust to jelly is:

This can be written as the fraction:

, or 

Example Question #1 : How To Find The Ratio Of A Fraction

In a solution,  of the fluid is water,  is wine, and  is lemon juice. What is the ratio of lemon juice to water?

Possible Answers:

Correct answer:

Explanation:

This problem is really an easy fraction division. You should first divide the lemon juice amount by the water amount:

Remember, to divide fractions, you multiply by the reciprocal:

This is the same as saying: 

Example Question #2 : How To Find The Ratio Of A Fraction

If  and , what is the ratio of  to ?

Possible Answers:

Correct answer:

Explanation:

To find a ratio like this, you simply need to make the fraction that represents the division of the two values by each other. Therefore, we have:

Recall that division of fractions requires you to multiply by the reciprocal:

which is the same as:

This is the same as the ratio:

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