Question

the nth term of a.p. is given by a[n] = 5n - 3 then the sum of first 10 terms will be? a.225 b.245 c.255 d.270

Answer 1

Given, nth term = 5n - 3

a(n) = 5n - 3




So,

a(1) = 5( 1 ) - 3
a = 5 - 3
a = 2


First term = a = 2






And,



a(10) = 5( 10 ) - 3
a(10) = 50 - 3
a(10) = 47





Sum of p terms = p( first term + last term ) / 2


So,


S(10) =10( 2 + 47 ) / 2
S(10) = 5( 49 )
S(10) = 245






$\boxed{ \bold{ \underline{ \: Sum \: of \: 10 \: terms \: is \: 245}}}$