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Question
The first term and the common difference of an A.P. is 10 and 5 respectively. Complete the following activity to find the sum of first 30 terms of the A. P.
`S_n=n/2[ ____+(n-1)d ]`
`∴ s_30=30/2[20+(30-1)xx _____ ]`
=`15[20+________]`
=`15xx165`
=_________
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Solution
`S_n=n/2[2a+(n-1)d]`
`∴ S_30=30/2[20+(30-1)xx5]`
=` 15[20+145]`
=`15xx165`
=`2475`
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