Is 7 over 8 less than 3 over 4?

No. Remember that when you multiply the top (numerator) and the bottom (denominator) of a fraction by the same number, the value of the fraction will remain the same. So, if we take your fraction, 3/4, and multiply the top and bottom by two (we are really multiplying by 2/2, which equals 1), we get 6/8. Simple examination now tells you that 7/8 is greater than 6/8. This method is called "finding a common denominator", and is very useful.