document.write( "Question 994082: How many terms are there and what is the sum for this series:
\n" ); document.write( "5+10+20+...5×(2^n)\r
\n" ); document.write( "\n" ); document.write( "Tried to answer and got number of erms as just \"n\" and hence the sum as (5(1-2^n))/-1 which doesn't seem right. \n" ); document.write( "

Algebra.Com's Answer #613287 by rothauserc(4718) $\"\"$ $\"About$

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5+10+20+...+(5×(2^n))
\n" ); document.write( "this is the summation as k varies from 0 to n of (5*2^k)
\n" ); document.write( "we use the fact that the partial sum, summation of k from 0 to n of 2^k = 2^(n+1) - 1, then
\n" ); document.write( "summation as k varies from 0 to n of (5*2^k) = 5*( 2^(n+1) - 1 )
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