Question 162667
Use a ratio
Ask yourself, 5 is to 25 as x is to 2. then solve for x
{{{5/25 = x/2}}}
{{{10/25 = x}}}
{{{0.4 = x}}}

Not sure how you get 0.4 apples, but that is what the math tells you. So in this case, you would have to do a little more thinking. There is no way to get 0.4 apples rotten. You either have a rotten apple or you don't. So, if you were asked, how many rotten apples do you 'expect' to find in a sample of two apples, your 'best bet' would be "none". You might actually have none, 1 or even 2. But the odds tell you, 0 is most likely based on the info you have handy.