Question 4082
 (note.. remember when adding or subtracting you need the same denominator 
 for the fractions).....

so... 

a.  2/3 + 3/4 =   (think 12) 
2/3 becomes 8/12  (3 divided by 12 = 4 x 2 = 8) and 3/4 becomes 9/12, then add em..... 8 + 9 = 17 and drop the denominator of 12 and you get 17/12, now reduce the imporper faction to 1 and 5/12.   

(the improper faction is... divide 12 by 17 and get 1, then subtract 12 from 17 and get 5, place it over the denominator)

b.  (3/5 + 4/7) + 2/5 = first the ( ) then the other... 
here you go.... 
with 3/5 and 4/7 think 35... and you should get 1 6/35.  BUT.. we are not done, now we must add 1 6/35 + 2/5 (ouch)!  ok.. lets keep the 35, because 5 will go into 35.... so....

1 6/35 remains and (2/5 changes to) 14/35 then lets add the top, 20/35 and drop the whole 1... and we get 1 20/35.  lets reduce because we can take 5 from each... 1 4/7... right???

c.  5/6 + 5/8 =   ok.. because we are using 6 and 8... we can see they go into 24 very nicely.... 

5/6 becomes 20/24 (remember the divide 24 / 6 = 4 x 5 = 20) and then the 5/8 becomes 15/24....  so lets add the 20/24 + 15/24 and we get 35/24.... remember the improper issue, we get 1 11/24.

Hope that helps.
Carl