Question 764843

a. 1+2+3+4+...+99

{{{1+99 = 100}}}
{{{99/2=49.5}}}

{{{sum=100*49.5= 4950}}}

b. 1+3+5+7+...+97

first find the sum 1+2+3+4+...+97

{{{1+97 = 98}}}
{{{98/2=49}}}

{{{sum=98*49= 4802}}} 

since you have only odd numbers, it will be half of  {{{4802}}} which is {{{2401}}}

so, the sum of 1+3+5+7+...+97 is {{{2401}}}