Sum
In an A.P, the first term is 25, nth term is -17 and the sum of n terms is 132. Find n and the common difference.
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Solution
First-term a = 25
nth term = -17 => last term l = -17
Sum of n terms = 132
`=> n/2 [a + l] = 132`
=> n(25 - 17) = 264
`=> n xx 8 = 264`
`=> n = 33`
Now l = -17
`=> a + (n - 1)d = -17`
`=> 25 + 32d = -17`
=> 32d = -42
`=> d = -42/32`
`=> d = -21/16`
Concept: Arithmetic Progression - Finding Sum of Their First ‘N’ Terms.
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