Question

find the sum of first 24 terms of an ap if it is known that a1 +a5+a10+a15+a20+a24=225

Answer 1

Let first term of AP be a and common difference be d.
Given,
a + (a+4d) + (a+9d) + (a+14d) + (a+19d) + (a+23d) = 225
i.e., 6a + 69d = 225

2a + 23d = 75 -------(1)

S24 = (24 / 2) × [2a + (24-1)×d] = 12 × [2a + 23d]
substituting (1),
S24 = 12 × 75 = 900

Answer 2

Answer:

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