A1+a5+a10+a16+a21+a25=900 in an
a.P , then the sum of first 25 terms us
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Here , a1 + a5+ a10+ a16+ a21 + a25 = 900
a + a+4d + a+9d + a + 15d + a+20d + a+ 24d = 900
6a + 72d = 900
If we divide the whole term by 6
a + 12d = 150
a = 150 - 12d
S25 = 25/2 ( 2x ( 150- 12d) + (25- 1 ) d
S25 = 25/2 ( 300 - 24d +24d)
S25 = 25/2 ( 300)
S25 = 25 × 150
S25 = 3750
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