Question 626226
let c be the number of chickens and r be the number of rabbits.
You are told
{{{c + r = 100}}} 
You are also told the total number of legs is 260. So
{{{2c + 4r = 260}}} since each chicken has 2 legs and each rabbit has 4
Use those two equations to solve for c
{{{r = 100 -c}}} from equation 1. 
{{{2c + 4r = 260}}} substitute in the value for r in the previous equation
{{{2c + 4(100-c) = 260}}} now simplfoy and solve for c
{{{2c + 400 - 4c = 260}}}
{{{-2c = -140}}}
{{{c = 70}}}
so you have 70 chickens and 30 rabbits. 
Check your answer, does 2*70 + 4*30 = 260?