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प्रश्न
Find the sum of those integers from 1 to 500 which are multiples of 2 as well as of 5.
उत्तर
Since, multiples of 2 as well as of 5 = LCM of (2, 5) = 10
But multiples of 2 as well as 5 from 1 to 500 is 10, 20, 30,..., 500.
∴ a = 10, d = 10, an = l = 500
∵ an = a + (n – 1)d = l
⇒ 500 = 10 + (n – 1)10
⇒ 490 = (n – 1)10
⇒ n – 1 = 49
⇒ n = 50
∵ Sn = `n/2(a + l)`
⇒ S50 = `50/2(10 + 500)`
= `50/2 xx 510`
= 50 × 255
= 12750
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