An arithmetic sequence is shown below. You are not given many terms of this sequence, but you do have enough to fill in the missing number. What number goes in the blank?

12, _, 54, ...

Someone show me how to slove this please . Gonna be asked many more and don't know how to work it out .

Question

An arithmetic sequence is shown below. You are not given many terms of this sequence, but you do have enough to fill in the missing number. What number goes in the blank?

12, _, 54, ...

Someone show me how to slove this please . Gonna be asked many more and don't know how to work it out .

anonymous · Answer

the missing number is 30, the difference is 21

12+21=33
30+21=54

anonymous · Answer

but there is a certain equation to solve problems like this .

noseboy908 · Answer

You're correct. It's t(n)=t1+d(n-1), where t1 is the first term, d is how much is added to a term to get the next one, and n is the number of the term. In this case, twelve is the first term, and 54 is the 3rd term. Thus, you can fill in t1 and n, as those are given. You can also fill in the left side, because you're given that t(n) there, and you know that that represents the t value for the highest number given. Make sense?

anonymous · Answer

Uhhh... nopee lol

noseboy908 · Answer

Ok, let me put it this way|dw:1401670688585:dw|

anonymous · Answer

21 :DDD

noseboy908 · Answer

Correct! Therefore you get the "d", which tells you how much to add to a number to get the next one.

anonymous · Answer

Thank you ! :)

noseboy908 · Answer

Welcome! This is exactly why I don't understand why people would just give answers. In the end it doesn't help in the long term.

anonymous · Answer

Exactly . I like to know what I'm doing so if a similar question pops up I don't ask again just do it myself with no problem .