An urn contains red and blue balls

MATHEMATICS · Subjective · AoPS · Mathematics · One-Variable Linear Equations · One-Variable Linear Equations

Problem

An urn contains red and blue balls. The probability of drawing a red ball is

0.4

. After 10 red balls and 5 blue balls are added to the urn, the probability of drawing a red ball becomes

0.45

. Find the original total number of balls in the urn.