Question

if the common difference of an ap is 13 then find a20-a15

Answer 1

Let the first term be a then,

a20 = a+19d

a15 = a+14d

a20-a15 = a+19d-a-14d

= 5d = 5×13 = 65

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Answer 2

Answer:

Let the first term of the AP be a.

an = a(n − 1)d

a₂₀ – a₁₅ = [a + (20 – 1)d] – [a + (15 – 1)d]

= 19d – 14d

= 5d

= 5 × 13

= 65