Examples with solutions for Series / Sequences: Complete the equation

Exercise #1

The sequence below is structured according to a term-to-term rule.

What is the first element?

?+? \text{?}+\text{?}

2+4 2+4

3+7 3+7

4+10 4+10

5+13 5+13

Video Solution

Step-by-Step Solution

We start with the right column in the exercises.

Between each number there is a jump of +3:4+3=7 4+3=7

7+3=10 7+3=10

Etcetera.

Now we move to the left column of the exercises.

Between each number there is a jump of +1:

2+1=3 2+1=3

3+1=4 3+1=4

Now we can figure out which exercise is missing:

The left digit will be:21=1 2-1=1

The right digit will be:43=1 4-3=1

And the missing exercise is:1+1 1+1

Answer

1+1 1+1

Exercise #2

Below is a sequence represented by squares. How many squares will there be in the 8th element?

Video Solution

Step-by-Step Solution

It is apparent, that for each successive number, a square is added in length and one in width.

Hence, the rule using the variable n is:

a(n)=n2 a(n)=n^2

Therefore, the eighth term will be:

n2=8×8=16 n^2=8\times8=16

Answer

64 64

Exercise #3

Below is the rule for a sequence written in terms of n n :

2n+2 2n+2

Calculate the value of the 11th element.

Video Solution

Step-by-Step Solution

We calculate by replacingn=11 n=11

2×11+2= 2\times11+2=

First we solve the multiplication exercise and then we add 2:

22+2=24 22+2=24

Answer

24 24

Exercise #4

Given a series whose first element is 15, each element of the series is less by 2 of its predecessor.

Is the number 1 an element of the series?

Video Solution

Step-by-Step Solution

We know that the first term of the series is 15.

From here we can easily write the entire series, until we see if we reach 1.  

15, 13, 11, 9, 7, 5, 3, 1

 

The number 1 is indeed an element of the series!

Answer

Yes

Exercise #5

A sequence has the following term-to-term rule:

n2 \frac{n}{2}

What is the the third term?

Video Solution

Step-by-Step Solution

The third term in the sequence is the term a3 a_3 :

an=n2 a_n= \frac{n}{2}

We need to substitute in the position of the term in the sequence:

n=3 n=3

Now, using our values:

an=n2n=3a3=32 a_{\underline{n}}= \frac{\underline{n}}{2} \\ n=\underline{3}\\ \downarrow\\ a_{\underline{3}}=\frac{\underline{3}}{2}

Now we substitute the position of the term in the sequence (3) in place of n. The substitution is shown with an underline in the expression above.

Therefore, the correct answer is answer C.

Answer

32 \frac{3}{2}

Exercise #6

10n9 10n-9

What are the fourth and fifth terms of the sequence above?

Video Solution

Step-by-Step Solution

The fourth and fifth terms in the sequence are the terms: a4,a5 a_4,\hspace{4pt}a_5 meaning in the general term formula given:

an=10n9 a_n=10n-9 we need to substitute the position (of the requested term in the sequence):

n=4 n=4 for - a4 a_4 and-

n=5 n=5 for-

a5 a_5 Let's do this for the fourth term:

an=10n9n=4a4=1049=409a4=31 a_{\underline{n}}= 10\underline{n}-9 \\ n=\underline{4}\\ \downarrow\\ a_{\underline{4}}= 10\cdot\underline{4}-9=40-9\\ a_4=31 when we substituted in place of n the position (of the requested term in the sequence): 4, substitution is shown with an underline in the expression above,

Similarly, for the fifth term, a5 a_5 we get:

a5=1059=509a5=41 a_{\underline{5}}= 10\cdot\underline{5}-9=50-9\\ a_5=41 which means that:

a4=31,a5=41 a_4=31,\hspace{4pt}a_5=41 Therefore the correct answer is answer A.

Answer

31, 41

Exercise #7

In the following series an

Given the series, y represents some term of the series

n represents the position of the term in the series

What are the first five members of the series?

an=3n+1 a_n=3n+1

Video Solution

Step-by-Step Solution

In order to determine the first five terms in the sequence simply insert their positions into the given formula as shown below:

an=3n+1 a_n=3n+1

We want to calculate the values of the terms:

a1,a2,a3,a4,a5 a_1,\hspace{4pt}a_2,\hspace{4pt}a_3,\hspace{4pt}a_4,\hspace{4pt}a_5

Let's start with the first term in the sequence,

an=3n+1 a_n=3n+1

We need to insert the position of whichever term that we want to find.

In this case we want to find the first term so we'll substitute as shown below:

n=1 n=1

Proceed to calculate:

an=3n+1n=1a1=31+1=4 a_{\underline{n}}= 3\underline{n}+1 \\ n=\underline{1}\\ \downarrow\\ a_{\underline{1}}=3\cdot\underline{1}+1=4

When we substituted the position in question in the place of n : the substitution is shown with an underline (as shown above),

Repeat this exact action for all the requested terms in the sequence, meaning for the second through fifth terms:

a2=32+1=7a3=33+1=10a4=34+1=13a5=35+1=16 a_{\underline{2}}=3\cdot\underline{2}+1=7 \\ a_{\underline{3}}=3\cdot\underline{3}+1=10 \\ a_{\underline{4}}=3\cdot\underline{4}+1=13 \\ a_{\underline{5}}=3\cdot\underline{5}+1=16 \\ For the second term a2 a_2 we substituted:n=2 n=2 in to the formula:

an=3n+1 a_n=3n+1

For the third term a3 a_3 we again substituted:n=3 n=3 and so on for the rest of the requested terms,

To summarize, we determined that the first five terms:

a1,a2,a3,a4,a5 a_1,\hspace{4pt}a_2,\hspace{4pt}a_3,\hspace{4pt}a_4,\hspace{4pt}a_5

in the given sequence, are:

4,7,10,13,16 4,\hspace{4pt}7,\hspace{4pt}10,\hspace{4pt}13,\hspace{4pt}16

Therefore, the correct answer is answer A.

Answer

4,7,10,13,16 4,7,10,13,16

Exercise #8

In a classroom there are 10 chairs numbered according to the constant property. Complete the series of chairs:

20 , 18

16 , 14

_ , _

8 , 6

4 , 2

Video Solution

Answer

12 , 10

Exercise #9

,,,Which shape appears in the fifth element of the sequence?

Video Solution

Answer

Exercise #10

,, Choose which represents the fourth element of the sequence.

Video Solution

Answer

Exercise #11

Which shape will appear in the fifth element of this sequence?

Video Solution

Answer

Exercise #12

Below is a sequence of exercises.

The sequence adheres to a certain term-to-term rule.

Complete the missing element (?):

6+5 6+5

5+4 5+4

?+? \text{?}+\text{?}

3+2 3+2

2+1 2+1

Video Solution

Answer

4+3 4+3

Exercise #13

Below is a sequence represented by squares. How many squares will there be in the 4th element?

Video Solution

Answer

16 16

Exercise #14

Below is a sequence represented by squares. How many squares will there be in the 5 element?

Video Solution

Answer

25 25

Exercise #15

Below is a sequence represented by squares. How many squares will there be in the 6th element?

Video Solution

Answer

36

Exercise #16

Below is a sequence represented with squares. How many squares will there be in the 7th element?

Video Solution

Answer

49 49

Exercise #17

Below is the rule for a sequence written in terms of n n :

2(n+4) 2(n+4)

Work out the value of the 9th element in the sequence.

Video Solution

Answer

26 26

Exercise #18

Below is the rule for a sequence in terms of n n :

2(2n2) 2(2n-2)

What is the value of the 7th element in the sequence?

Video Solution

Answer

24 24

Exercise #19

What is the shape of the fourth element?

,,

Video Solution

Answer

Exercise #20

Below is a sequence of exercises.

The sequence adheres to a certain term-to-term rule. Complete the missing element (?):

18+49 18+49

14+37 14+37

?+? \text{?}+\text{?}

6+13 6+13

2+1 2+1

Video Solution

Answer

10+25 10+25