Julian starts with 3/5 of a cookie and gives away to friend. And the amount it 1/2 of the cookie.
We subtract. Because we are taking away a piece of cookie from the cookie.
[tex] \frac{3}{5} - \frac{1}{2} = \frac{x}{10} - \frac{x}{10} = \frac{6}{10} - \frac{5}{10} = \frac{1}{10} [/tex]
