Question

the 10th and 18th terms of an AP are 41 and 73.find its 28th term

Answer 1

Given : a + 9d = 41 and a + 17d = 73 (a = first term d = common difference)
Subtracting the two equations, we get 8d = 32 
Therefore, d = 4. Put d = 4 in the first equation.
a + 36 = 41 ⇒ a = 5

a₂₈ = a + 27d = 5 + 27*4 = 113.


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Answer 2

41=a+9d......(1)
73=a+17d........(2)
.... (2)-.... (1), gives
32=8d
d=4
therefore, a=5
Now, a28 = 5+ 27(4) =113