Question 35399
To add fractions you must have a "common denominator"--an integer that is a common multiple of the denominators of two or more fractions 
an attribute that is common to all members of a category.  So here {{{1/4 + 3/7 + 1/8}}} We find that 56 is a common denominator for these numbers (you can find this by testing a few numbers) so {{{((1*14)/(4*14))+((3*8)/(7*8))+((1*7)/(8*7))=45/56}}}.

Hope this helps,
lyra