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An AP has 20 terms. The 5th term from the beginning plus the 5th term from the end is 64. Find the sum of all 20 terms.

Class 10Properties and Selection of AP TermsAlgebra — Sequences

A64
B1,280
C320
D640

Step-by-Step Solution

Terms equidistant from the ends have the same sum, so

a_{1} + a_{20} = 64. S_{20} = \frac{20}{2} (a_{1} + a_{20}) = 10 \times 64 = 640

.

Answer: D) 640

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