The sum of two numbers is 203203. the difference between them is 3131. find the two numbers.

let the first number be x
let the second number be y

x+y=203203eqn1
x-y=3131eqn2
subtract eqn2 from eqn1. you'll have
2y=200072
y=100036
substitute y=100036 in eqn1, you'll have
x+(100036)=203203
x=203203-100036
x=103167
∴ x(the first number)=103167
   y(the second number)=100036