SSAT Upper Level Math : Arithmetic Sequences

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

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Example Questions

Example Question #4 : How To Find The Nth Term Of An Arithmetic Sequence

An arithmetic sequence begins as follows:

\displaystyle 1 \frac{1}{7}, 3 \frac{1}{4},...

Which of the following is the first term greater than 100?

Possible Answers:

The forty-ninth term

The fifty-first term

The fiftieth term

The forty-eighth term

The forty-seventh term

Correct answer:

The forty-eighth term

Explanation:

The common difference of the sequence is

\displaystyle 3 \frac{1}{4} - 1 \frac{1}{7} = 2\frac{3}{28}

so the \displaystyle nth term of the sequence is

\displaystyle a_{n} = 1\frac{1}{7} + \left ( 2\frac{3}{28} \right ) (n-1)

To find out the minimum value for which \displaystyle a_{n} > 100, set up this inequality:

\displaystyle 1\frac{1}{7} + \left ( 2\frac{3}{28} \right ) (n-1) > 100

\displaystyle 1\frac{1}{7} + \left ( 2\frac{3}{28} \right ) n -2\frac{3}{28} > 100

\displaystyle \left ( 2\frac{3}{28} \right ) n - \frac{27}{28} > 100

\displaystyle \left ( 2\frac{3}{28} \right ) n > 100 \frac{27}{28}

\displaystyle n > 100 \frac{27}{28} \div 2\frac{3}{28} = 47 \frac{54}{59}

The correct response is the forty-eighth term.

 

Example Question #3 : How To Find The Nth Term Of An Arithmetic Sequence

The tenth and twelfth terms of an arithmetic sequence are 8.4 and 10.2. What is its first term?

Possible Answers:

\displaystyle 0.9

\displaystyle 1.2

\displaystyle 1.8

\displaystyle 0.3

\displaystyle -0.6

Correct answer:

\displaystyle 0.3

Explanation:

The \displaystyle nth term of an arithmetic sequence with initial term \displaystyle a_{1} and common difference \displaystyle d is defined by the equation

\displaystyle a_{n} = a_{1}+ (n-1)d

Since the tenth and twelfth terms are two terms apart, the common difference can be found as follows:

\displaystyle a_{10}+2d=a_{12}

\displaystyle 8.4+2d=10.2

\displaystyle 8.4+2d- 8.4=10.2 - 8.4

\displaystyle 2d=1.8

\displaystyle d = 0.9

 

Now, we can set \displaystyle n = 10, d = 0.9 in the sequence equation to find \displaystyle a_{1}:

\displaystyle a_{n} = a_{1}+ (n-1)d

\displaystyle a_{10} = a_{1}+ (10-1)0.9

\displaystyle 8.4 = a_{1}+ 9 \cdot 0.9

\displaystyle 8.4 = a_{1}+ 8.1

\displaystyle 8.4 - 8.1 = a_{1}+ 8.1 - 8.1

\displaystyle a_{1} = 0.3

Example Question #6 : How To Find The Nth Term Of An Arithmetic Sequence

The eleventh and thirteenth terms of an arithmetic sequence are, respectively, 11 and 14. Give its first term.

Possible Answers:

\displaystyle 1\frac{1}{2}

\displaystyle -5\frac{1}{2}

\displaystyle -22

\displaystyle -4

\displaystyle -2\frac{1}{2}

Correct answer:

\displaystyle -4

Explanation:

The \displaystyle nth term of an arithmetic sequence with initial term \displaystyle a_{1} and common difference \displaystyle d is defined by the equation

\displaystyle a_{n} = a_{1}+ (n-1)d

Since the eleventh and thirteenth terms are two terms apart, the common difference can be found as follows:

\displaystyle a_{11}+2d=a_{13}

\displaystyle 11+2d=14

\displaystyle 11+2d -11=14 -11

\displaystyle 2d = 3

\displaystyle d = \frac{3}{2}

 

Now, we can set \displaystyle n = 11, d =\frac{3}{2} in the sequence equation to find \displaystyle a_{1}:

\displaystyle a_{11} = a_{1}+ (11-1) \frac{3}{2}

\displaystyle 11= a_{1}+ 10 \cdot \frac{3}{2}

\displaystyle 11= a_{1}+ 15

\displaystyle 11- 15= a_{1}+ 15 - 15

\displaystyle a_{1} = -4

Example Question #42 : Sequences And Series

The lengths of the sides of ten squares form an arithmetic sequence. One side of the smallest square measures eight inches; one side of the second-smallest square measures one foot. 

Give the area of the largest square.

Possible Answers:

576 square inches

1,936 square inches

484 square inches

784 square inches

2,304 square inches

Correct answer:

1,936 square inches

Explanation:

Let \displaystyle a_{n} be the lengths of the sides of the squares in inches. \displaystyle a_{1} = 8 and \displaystyle a_{2} = 12, so their common difference is

\displaystyle d = a_{2} - a_{1} = 12 - 8 = 4

The arithmetic sequence formula is 

\displaystyle a_{n} = a_{1} + (n-1)d

The length of a side of the largest square - square 10 - can be found by substituting \displaystyle a_{1} = 8, n= 10, d = 4:

\displaystyle a_{10} =8+ (10-1) 4 = 8 + 9 \cdot 4 = 8 + 36 = 44 

The largest square has sides of length 44 inches, so its area is the square of this, or \displaystyle A = 44^{2} = 1,936 square inches.

Example Question #11 : Nth Term Of An Arithmetic Sequence

An arithmetic sequence begins as follows:

\displaystyle 12, 19, 26, 33,...

Give the thirty-second term of this sequence.

Possible Answers:

\displaystyle 250

\displaystyle 229

\displaystyle 243

\displaystyle 236

\displaystyle 222

Correct answer:

\displaystyle 229

Explanation:

The \displaystyle nth term of an arithmetic sequence with initial term \displaystyle a_{1} and common difference \displaystyle d is defined by the equation

\displaystyle a_{n} = a_{1}+ (n-1)d

The initial term in the given sequence is

\displaystyle a_{1} = 12;

the common difference is

\displaystyle d = 19-12= 7;

We are seeking term \displaystyle n = 32.

This term is  

\displaystyle a_{32} = 12+ (32-1) 7

\displaystyle a_{32} = 12+ 31 \cdot 7 = 12+ 217 = 229

 

Example Question #541 : Number Concepts And Operations

An arithmetic sequence begins as follows:

\displaystyle \frac{2}{5} , \frac{7}{10}, 1, 1 \frac{3}{10}, ...

Give the thirty-third term of this sequence.

Possible Answers:

\displaystyle 9\frac{9}{10}

\displaystyle 10\frac{1}{10}

\displaystyle 9\frac{4}{5}

\displaystyle 10 \frac{1}{5}

The correct answer is not given among the other four responses.

Correct answer:

The correct answer is not given among the other four responses.

Explanation:

The \displaystyle nth term of an arithmetic sequence with initial term \displaystyle a_{1} and common difference \displaystyle d is defined by the equation

\displaystyle a_{n} = a_{1}+ (n-1)d.

The initial term in the given sequence is

\displaystyle a_{1} = \frac{2}{5};

the common difference is

\displaystyle d = \frac{7}{10} - \frac{2}{5} = \frac{7}{10} - \frac{4}{10} = \frac{3}{10}.

We are seeking term \displaystyle n = 33.

Therefore,

\displaystyle a_{33} = \frac{2}{5}+ (33-1) \frac{3}{10}

\displaystyle = \frac{2}{5}+ (32) \frac{3}{10}

\displaystyle = \frac{2}{5}+ \frac{96}{10}

\displaystyle = \frac{2}{5}+ \frac{48}{5}

\displaystyle = \frac{50}{5} = 10,

which is not among the choices.

Example Question #21 : Arithmetic Sequences

What is the value of x in the sequence below?

\displaystyle 99, 33, 11, x

Possible Answers:

\displaystyle 11\frac{1}{3}

\displaystyle 3\frac{2}{3}

\displaystyle \frac{11}{2}

\displaystyle 4

Correct answer:

\displaystyle 3\frac{2}{3}

Explanation:

In this sequence, each subsequent number is equal to one third of the preceding number. 

One third of 11 is equal to:

\displaystyle \frac{11}{3}=3\frac{2}{3}

Therefore, the correct answer is: \displaystyle 3\frac{2}{3}

Example Question #22 : Arithmetic Sequences

Find the next term of the arithmetic sequence:

 

\displaystyle 24, 29, 34, ?

Possible Answers:

\displaystyle 36

\displaystyle 30

\displaystyle 39

\displaystyle 38

Correct answer:

\displaystyle 39

Explanation:

The common difference for this sequence is \displaystyle 5. To find the next number in the sequence, add \displaystyle 5 to the last given number.

\displaystyle 34+5=39

Example Question #23 : Arithmetic Sequences

Find the next term of this arithmetic sequence:

\displaystyle -15, -8, -1, ?

Possible Answers:

\displaystyle 4

\displaystyle 3

\displaystyle 6

\displaystyle 5

\displaystyle 7

Correct answer:

\displaystyle 6

Explanation:

The common difference for this sequence is \displaystyle 7. Add this to the last given term to find the next one.

\displaystyle -1+7=6

Example Question #24 : Arithmetic Sequences

Find the next term of the arithmetic sequence:

\displaystyle -4, 5, 14, ?

Possible Answers:

\displaystyle 23

\displaystyle 24

\displaystyle 20

\displaystyle 22

Correct answer:

\displaystyle 23

Explanation:

The common difference is \displaystyle 9. Add this to the last given term to find the next term.

\displaystyle 14+9=23

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