, we obviously need to subtract 3 1/4 - 3 1/9. We can leave the 3 out for now and just subtract 1/4 - 1/9. First, we need to find a common denominator. We must find the LCM of 4 and 9. 4, 8, 12, 16, 20, 24, 28, 32, 36, 40 9, 18, 27, 36, 45 The LCM is 36. 1/4 = ?/36. Since 4 x 9 = 36, we must multiply 1 x 9 to get 9/36. We do the same with 1/9. 1/9 = ?/36. 9 x 4 = 36. 1 x 4 = 4, so we have 4/36. 9/36 - 4/36 = 5/36 We need 5/36 of a cup! Hope this helps!