SOLUTION: The 5th and 10th term of AP are 23 and 48 respectively.find its 18th term?

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Question 1073594: The 5th and 10th term of AP are 23 and 48 respectively.find its 18th term?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a%5Bn%5D=a%5B1%5D%2B%28n-1%29d
So,
a%5B5%5D=a%5B1%5D%2B%285-1%29d=a%5B1%5D%2B4d=23
a%5B10%5D=a%5B1%5D%2B%2810-1%29d=a%5B1%5D%2B9d=48
Subtracting the two equations,
a%5B1%5D%2B9d-a%5B1%5D-5d=48-23
5d=25
Solve for d, then use either equation to solve for a%5B1%5D.
Then find,
a%5B18%5D=a%5B1%5D%2B17d