MSNBC reported that at least three-fourths of the 55 companies that advertise nationally on television will cut spending on commericals because of electronics that let viewers record programs and edit out commericals. Does this mean at least 41, or at least 42, of the companies will cut spending on commericals?

I'm a little surprised that the problem mentioned three-fourths instead of three-quarters...

Anyway, back to the question.

\frac34 \times 55 = \frac{165}{4} = 41.25

As you can see, the remainder is less than half (0.5) and thus, we take it to the nearest integer, which is 41.

If it happened to be 41.8, then, you would have taken it as being 42 (it's closer to 42 than 41).

If it happened to be 41.5, you then take it as being 42.

As soon as it reaches 0.5, you take the integer which comes afterwards.
If you get 41.499999, you still take the previous integer.

I hope it helps! :)