Find the missing term of the following arithmetic sequence. ...7, ____, 15, ...

Answer 1

In an arithmetic sequence the pattern adds/subtracts by the same amount each time.

Let's call this value that you add each time "x"

If the starting value is 7

Then the next value is 7+x

The next is 7+x+x

The next is 7+x+x+x

and so forth

Since we have the second term

we can set 7+x+x=15

First we combine the like terms

7+2x=15

subtract 7 from each side

2x=8

and we get x=4

So we can go fill in now that 7+4=11 for the second term

and see our pattern of 7, 11, 15 is an arithmetic sequence as each value adds 4 to the previous one.

Answer 2

15 = 7 + 2d

8 = 2d

4 = d

7, 11, 15