PSAT Math : How to add fractions

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Add Fractions

Jesse has a large movie collection containing X movies. 1/3 of his movies are action movies, 3/5 of the remainder are comedies, and the rest are historical movies. How many historical movies does Jesse own?

Possible Answers:

(11/15)*X

(2/5)*X

(4/15)*X

(7/12)*X

(3/9)*X

Correct answer:

(4/15)*X

Explanation:

1/3 of the movies are action movies. 3/5 of 2/3 of the movies are comedies, or (3/5)*(2/3), or 6/15. Combining the comedies and the action movies (1/3 or 5/15), we get 11/15 of the movies being either action or comedy. Thus, 4/15 of the movies remain and all of them have to be historical.

Example Question #21 : Operations With Fractions

If x = 1/3 and y = 1/2, find the value of 2x + 3y.

Possible Answers:

6/5

13/6

2

5/6

1

Correct answer:

13/6

Explanation:

Substitute the values of x and y into the given expression:

2(1/3) + 3(1/2)

= 2/3 + 3/2

= 4/6 + 9/6

= 13/6

Example Question #22 : Operations With Fractions

Alternating1

Possible Answers:

\dpi{100} -\frac{43}{60}

\dpi{100} \frac{17}{60}

\dpi{100} -\frac{47}{60}

\dpi{100} \frac{43}{60}

\dpi{100} \frac{47}{60}

Correct answer:

\dpi{100} \frac{47}{60}

Explanation:

Alternating2

Alternating3

Example Question #131 : Fractions

Solve \frac{3}{7}+\frac{5}{8}-\frac{1}{2}\displaystyle \frac{3}{7}+\frac{5}{8}-\frac{1}{2}.

Possible Answers:

\frac{33}{56}\displaystyle \frac{33}{56}

\frac{7}{8}\displaystyle \frac{7}{8}

\frac{5}{7}\displaystyle \frac{5}{7}

\frac{31}{56}\displaystyle \frac{31}{56}

Correct answer:

\frac{31}{56}\displaystyle \frac{31}{56}

Explanation:

Finding the common denominator yields \frac{24}{56}+\frac{35}{56}-\frac{28}{56}\displaystyle \frac{24}{56}+\frac{35}{56}-\frac{28}{56}. We can then evaluate leaving \frac{31}{56}\displaystyle \frac{31}{56}.

Example Question #2 : How To Add Fractions

What is the solution, reduced to its simplest form, for x = \frac{7}{9}+\frac{3}{5}+\frac{2}{15}+\frac{7}{45}} ?

Possible Answers:

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

x =2\displaystyle x =2

x = \frac{7}{15}\displaystyle x = \frac{7}{15}

x = \frac{75}{45}\displaystyle x = \frac{75}{45}

x = \frac{115}{45}\displaystyle x = \frac{115}{45}

Correct answer:

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

Explanation:

x=\frac{7}{9}+\frac{3}{5}+\frac{2}{15}+\frac{7}{45}=\frac{35}{45}+\frac{27}{45}+\frac{6}{45}+\frac{7}{45}=\frac{75}{45}=\frac{5}{3}\displaystyle x=\frac{7}{9}+\frac{3}{5}+\frac{2}{15}+\frac{7}{45}=\frac{35}{45}+\frac{27}{45}+\frac{6}{45}+\frac{7}{45}=\frac{75}{45}=\frac{5}{3}

Example Question #3 : How To Add Fractions

What is the sum of \displaystyle \small \frac{4}{5} and \displaystyle \small 2 \frac{5}{6}?

Possible Answers:

\displaystyle \small \frac{109}{30}

\displaystyle \small \frac{49}{109}

\displaystyle \small \frac{79}{30}

\displaystyle \small \frac{30}{109}

\displaystyle \small \frac{49}{12}

Correct answer:

\displaystyle \small \frac{109}{30}

Explanation:

We can begin by eliminating the obviously wrong answers. We know that the sum of the two fractions will be more than 1, so the answer choices \displaystyle \tiny \tiny \frac{49}{109} and \displaystyle \small \frac{30}{109} are out. Now, let's add the two fractions:

Begin by converting \displaystyle \small 2 \frac{5}{6} to \displaystyle \tiny \frac{17}{6}.

Now find the common denominator of \displaystyle \small \frac{4}{5} and \displaystyle \tiny \frac{17}{6}. The least common multiple of 5 and 6 is 30, so 30 is the common denominator. Now alter both fractions so that they use the common denominator:

\displaystyle \tiny \small \frac{4}{5}= \frac{4*6}{5*6}=\frac{24}{30}

 \displaystyle \tiny \small \frac{17}{6}=\frac{17*5}{6*5}=\frac{85}{30}

Now we can easily add the two fractions together:

\displaystyle \small \frac{24}{30}+\frac{85}{30}=\frac{109}{30}

The answer is \displaystyle \small \frac{109}{30}.

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