SSAT Middle Level Math : How to find mean

Study concepts, example questions & explanations for SSAT Middle Level Math

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Example Questions

Example Question #81 : Statistics & Probability

In a group of 4 books, the average number of pages is is 10.  Juan adds a book with 20 pages to the group.  What is the new average number of pages?

Possible Answers:

\(\displaystyle 30\)

\(\displaystyle 20\)

\(\displaystyle 12\)

\(\displaystyle 15\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 12\)

Explanation:

If the average of 4 books was 10, then the total number of pages was \(\displaystyle 4\times10 =40\). Adding in the 20 new pages, but now dividing by 5 you get \(\displaystyle 60/5 = 12\).

Example Question #1 : Data Analysis

Give the mean of the data set (nearest tenth, if applicable): 

\(\displaystyle \left \{ 56,78,98,85,77,73 \right \}\)

Possible Answers:

\(\displaystyle 77.3\)

\(\displaystyle 77.8\)

\(\displaystyle 76.5\)

\(\displaystyle 75.7\)

\(\displaystyle 79.6\)

Correct answer:

\(\displaystyle 77.8\)

Explanation:

Add the six elements and divide the sum by 6:

\(\displaystyle 56 + 78 + 98 + 85 +77 + 73 = 467\)

\(\displaystyle 467 \div 6 \approx 77.8\)

Example Question #82 : Statistics & Probability

Find the mean of this set of numbers:

54, 41, 99, 120, 66.

Possible Answers:

\(\displaystyle 80\)

\(\displaystyle 79\)

\(\displaystyle 99\)

\(\displaystyle 76\)

Correct answer:

\(\displaystyle 76\)

Explanation:

Firrst, add the numbers:

\(\displaystyle 54+41+99+120+66=380\)

Then, divide by the amount of numbers in the set:

\(\displaystyle 380\div 5=76\)

Answer: The mean is 76.

Example Question #2 : Data Analysis

Give the mean of the following eight scores: 

\(\displaystyle \left \{ 61, 67, 80, 72, 76, 73, 90, 68 \right \}\)

Possible Answers:

\(\displaystyle 73\)

\(\displaystyle 72.5\)

\(\displaystyle 75.5\)

\(\displaystyle 72.875\)

\(\displaystyle 73.375\)

Correct answer:

\(\displaystyle 73.375\)

Explanation:

Divide the sum of the scores by eight:

\(\displaystyle \frac{ 61+ 67+80+72+76+73+90+ 68}{8} = \frac{ 587}{8} = 73.375\)

Example Question #1 : Mean

Give the mean of the following nine scores: 

\(\displaystyle \left \{ 61, 67, 80, 72, 76, 73, 90, 68, 70 \right \}\)

Possible Answers:

\(\displaystyle 75.5\)

\(\displaystyle 72\)

\(\displaystyle 68\)

\(\displaystyle 72.5\)

\(\displaystyle 73\)

Correct answer:

\(\displaystyle 73\)

Explanation:

Divide the sum of the scores by nine:

\(\displaystyle \frac{ 61 + 67+ 80+ 72+ 76+73+90+68+70}{9} = \frac{ 657}{9} = 73\)

Example Question #1 : Find Median

Give the median of the following eight scores: 

\(\displaystyle \left \{ 61, 67, 80, 72, 76, 73, 90, 68 \right \}\)

Possible Answers:

\(\displaystyle 72.5\)

\(\displaystyle 72\)

\(\displaystyle 73.375\)

\(\displaystyle 75.5\)

\(\displaystyle 73\)

Correct answer:

\(\displaystyle 72.5\)

Explanation:

Arrange the scores from least to greatest.

\(\displaystyle \left \{ 61, 67, 68, 72, 73, 76, 80, 90 \right \}\)

There are an even number (eight) of scores, so the median is the arithmetic mean of the middle two scores, 72 and 73. This makes the median

\(\displaystyle \frac{72 + 73}{2} = 72.5\)

Example Question #2 : Mean

The average age of 4 people is 12.  What will be the sum of their ages in 3 years?

Possible Answers:

\(\displaystyle 24\)

\(\displaystyle 15\)

\(\displaystyle 12\)

\(\displaystyle 60\)

\(\displaystyle 56\)

Correct answer:

\(\displaystyle 60\)

Explanation:

The current sum of their ages is \(\displaystyle 12\times 4=48\).  Since all 4 people will gain 3 years in age, we have to add 12 to the current sum.

Example Question #4 : How To Find Mean

What is the mean of the values \(\displaystyle 34\), \(\displaystyle 40\), \(\displaystyle 1\), \(\displaystyle 9\)\(\displaystyle 21?\)

Possible Answers:

\(\displaystyle 40\)

\(\displaystyle 5\)

\(\displaystyle 34\)

\(\displaystyle 21\)

\(\displaystyle 105\)

Correct answer:

\(\displaystyle 21\)

Explanation:

The mean of a set of values can be calculated by adding the values together and dividing by the number of values: \(\displaystyle \frac{34+40+1+9+21}{5}=21\)

Example Question #1 : Mean

On the first four exams, Charley scored 92, 88, 76, and 74. Charley wants to have a test average of 85%.  What must Charley score on the fifth exam to average 85%?

Possible Answers:

100%

82%

95%

90%

85%

Correct answer:

95%

Explanation:

The summation of the first four exams equals 330.  Using the equation for average, Charley needs to get a 95 on the last exam.

 \(\displaystyle \frac{330+x}{5}=85\)

\(\displaystyle 330+x=85*5=425\)

\(\displaystyle x=425-330=95\)

\(\displaystyle x=95\)

 

Example Question #4 : Find Measures Of Center, Variability, And Patterns In Data: Ccss.Math.Content.6.Sp.B.5c

Give the mean of the following data set:

\(\displaystyle \left \{1, 2, 3, 3, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, 9, 10 \right \}\)

Possible Answers:

\(\displaystyle 5.375\)

\(\displaystyle 5.0625\)

\(\displaystyle 6\)

\(\displaystyle 5.5\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 5.0625\)

Explanation:

Since there are 16 elements, divide their sum by 16 to get the mean:

\(\displaystyle (1+ 2+ 3+ 3+ 4+ 4+ 4+ 5+ 5+ 6+ 6+ 6+ 6+ 7+ 9+ 10) \div 16 = 81 \div 16 = 5.0625\)

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