The sum from tenth terms and twenty terms inclusive of AP is 1155,find the common difference if the first term is 7.
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given a10+a30=1155...........(1)
wkt an=a+(n-1)d
given a=7
a10=7+9d
a20=7+19d
therefore
14+28d=1155[from (1)]
28d=1141
d=40.75
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