4.
4)
5 * (1/5 - 1/7) = 5 * 1/5 - 5 * 1/7,
5.
3)
2/5 * (9/13 * 13/17) - 3/5 * (5/11 * 11/17) =
= 2/5 * 9/17 - 3/5 * 5/17 =
= 18/75 - 15/75 = 3/75 = 1/25
