Question 329266
13, because, if you chose 12 it is possible, though very unlikely, to have
gotten 8 reds and 4 greens, and no blues, or 8 reds, 4 blues, and no greens.  But by the 13th you must have at least one of every color.


<pre><b>
If 300 beans cost you x dollars. How many beans can you purchase
for 50 cents at the same rate?

"300 beans IS TO x dollars AS y beans IS TO {{{1/2}}} dollar."

300 beans IS TO $x AS y beans IS TO $.50.

In mathspeak, "IS TO" means "OVER", and "AS" means "EQUALS"
 
300 beans OVER $x EQUALS y beans OVER $.50.

{{{300/x}}}{{{""=""}}}{{{y/.50}}}

Cross multiply:

{{{xy}}}{{{""=""}}}{{{300*.50}}}

{{{xy}}}{{{""=""}}}{{{150}}}

Divide both sides by x:

{{{y}}}{{{""=""}}}{{{150/x}}} beans,

Edwin</pre>