1) 19/25 + (1/15 + 1/25) = 19/25 + (2/25 + 1/25) = 19/25 + 3/25 = 22/25
2) (19/28 + 1/7) - 13/28 = 19/28 + 4/28 - 13/28 = 20/28 - 13/28 = 7/28
3) (7/16 + 5/18) + (1/16 + 1/18) = 7/16 + 5/18 + 1/16 + 1/18 = 49/144 + 40/144 + 9/144 + 8/144 = 106/144 = 53/72
4) 10/21 + 19/42 + 4/21 - 5/42 = 20/42 + 19/42 + 8/42 - 5/42 = 42/42 = 1
1) 19/25 + (1/15 + 1/25) = 19/25 + (2/25 + 1/25) = 19/25 + 3/25 = 22/25
2) (19/28 + 1/7) - 13/28 = 19/28 + 4/28 - 13/28 = 20/28 - 13/28 = 7/28
3) (7/16 + 5/18) + (1/16 + 1/18) = 7/16 + 5/18 + 1/16 + 1/18 = 49/144 + 40/144 + 9/144 + 8/144 = 106/144 = 53/72
4) 10/21 + 19/42 + 4/21 - 5/42 = 20/42 + 19/42 + 8/42 - 5/42 = 42/42 = 1