+302 find the 20th term from the last term of the A.P: 3,8,13,,,,,253
+37163 Common difference between terms is 5 (8-3 = 5 13-8 = 5 etc)
this is of the form 3 + 5 (n-1)
3 + 5n -5 = 5n-2 where n= number of the term
20th term 5(20)-2 = 98
+129850 Good idea.....!!!
The last term is 253
And the common difference in terms is 5
So......the 20th term from the last =
253 - 5(n - 1) =
253 - 5(20 - 1) =
253 - 5(19) =
158
+129850 I suppose that you're technically correct......the common difference is -5 [ we are subtracting 5 each time ]
+37163 Chris pointed out to me that I mis-read your question.....
I will continue the way I started
we have 5n-2 gives the nth term
253 = 5n-2
255 = 5n
yields n = 51st term for 253 20 terms before this would be 31st term
5(31)-2 = 153 = 20 terms before 253
I think Chris answer may be the 19th before 253
if you use his equation the tem that is ONE before would be 253 - 5(1-1) = 253 which would be incorrect.
