Question

Luke has a blue ball and red balls.
Every day, he wins 2 blue balls and loses 3 red ones.
After 5 days, he has the same amount of blue and red balls.
After 9 days, he has twice as many blue balls as red balls.
How many red balls did he have at the beginning?

Answer 1

let the number of red balls be x
let the number of blue balls be y
after 5 days
there are y+10 blue balls and x-15 red balls
so
y+10 = x-15
y+35 = x

after 9 days
there are y+18 blue balls and x-27 red balls
y+18 = 2*(x-27)
y+18 = 2x -54
y+72 = 2x
subtituting
x - 35+72 = 2x
37 = x

Comments

10+15=25
Not 35