Question

Find the three arithmetic means between 7 and 21. 7,___,___,___,21

Answer 1

I was waiting to see what Cinnamon was going to type before I answered.

Answer 2

can you help me though?

Answer 3

I done these today but I was trying to work it out, dont think its working my way

Answer 4

Take the difference between the last term and the first term and divide it by 5 since are trying to find the first 5 terms in a sequence with a common difference.

Answer 5

-2.8?

Answer 6

Actually 2.8, but yes.

Answer 7

ok now what?

Answer 8

Now add that to 7, to get your next term, and continue to do so for each of the next two terms.

Answer 9

7, 9.8, 12.6, 15.4, 18.2 wait thats not right though i need 21 for the 5th term

Answer 10

Hang on..

Answer 11

the difference is 3.5

Answer 12

YAYYY THAT WORKED

Answer 13

My bad, I forgot to divide by n-1, not n...lol

Answer 14

so the answer is 7,10.5, 14, 17.5, 21!!!! :) thank you

Answer 15

n=5

Answer 16

Very welcome! :)

Answer 17

your formula is \[a _{n}=a _{1}+(n-1)d\]

Answer 18

We know a_1=7 and we know a_n=21 with n=5, so we are only missing d.

Answer 19

21=7+(5-1)d means 14=4d which results in d=3.5 as detailed by cinnamonbuns

Answer 20

Good job everyone! (Except for @calmat01 he needs to go to the corner!