Question

find the missing terms in each sequence 3, [?], [?], 20 (arithmetic)

Answer 1

trial and error. 8.5 :DD

Answer 2

that is the common difference by the way

Answer 3

can i get the formula to find it, so i cant get it in my brain

Answer 4

Let's say you have the following sequence:
2, 4, 6, 8
Obviously the common difference is 2, since that is the difference between any number and the previous number.

Answer 5

there is two blanks between 3 and 20 so I cant get the common differnce

Answer 6

We're working on that. be patient.
Let's call the common difference d.
The terms would be 2, 2 + d, 2 + 2d , 2 + 3d

Answer 7

ok

Answer 8

Now take the last term, 2 + 3d. Set that equal to 8.
2 + 3d = 8
Solve for d
3d = 6
d = 2
As you can see, we found the common difference in my example to be 2, which we already know is correct.

Answer 9

Now try the same thing with your sequence.

Answer 10

why did you set is equal to 8?

Answer 11

u still there?

Answer 12

In my example, the last term was 8.

Now let's go back to your problem.
3, [?], [?], 20
3, 3 + d, 3 + 2d, 3 + 3d

Notice that in your problem, 3 + 3d must equal 20.
With that, you can write and solve and equation to find d.
Once you know d, you can find the two middle terms.

Answer 13

d = common difference if correct?

Answer 14

Yes.

Answer 15

d=5.6666

Answer 16

Correct.
Now you can find the two middle terms.

Answer 17

thanks a ton

Answer 18

You're welcome.

Answer 19

ok ive got a pretty touch one :

[?], [?], 2, [?], [?], 53.

Answer 20

Pretend the sequence starts at the 2.
Use the 2 and the 53 exactly like we did the problem and the example before.

Answer 21

Then, once you find d, use d to find all missing terms.