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What is the 23rd term of the arithmetic sequence where a1 = 7 and a5 = 21?

Question

Please and thank youuuuu!
 What is the 23rd term of the arithmetic sequence where a1 = 7 and a5 = 21?

cwrw238 · Answer

first find the common difference 
can u do that?

anonymous · Answer

Im not really sure what you mean?

anonymous · Answer

you have to find how far the first number is from the second one. that's the common difference.

cwrw238 · Answer

arithmetc series can be written as

a, a+d, a+ 2d, a + 3d, ....
common difference d is added to each term to get the next term

cwrw238 · Answer

a1 is first term and a5 is the fifth so 4 'd's have been added to get from a1 to a5

do you follow that ?

anonymous · Answer

got it

cwrw238 · Answer

ok so if we work out a5 - a1 and divide by 4 we get d
so
21-7 / 4 = 14/4 = 3.5

d = 3.5

cwrw238 · Answer

general form for nth term = a1 + (n-1)d
so 23rd term = 7 + (23-1)3.5
  = 7 + 22*3.5

anonymous · Answer

84, thanks!

cwrw238 · Answer

thats right  - yw