svetazuna А)
2/5 : 4 = 2/5 * 1/4 = 2/20 = 1/10,
пров.:
1/10 * 4 = 4/10 = 2/5,

б)
8/9 : 2 = 8/9 * 1/2 = 8/18 = 4/9,
пров.:
4/9 * 2 = 8/9,

в)
15/16 : 5 = 15/16 * 1/5 = 3/16,
пров.: 
3/16 * 5 = 15/16,

г)
7/30 : 2 = 7/30 * 1/2 = 7/60,
пров.: 
7/60 * 2 = 14/60 = 7/30,