a)10x=52, x=52/10, x=26/5, x=5.2.ver; 5*5.2/4=13/2, 26/4=13/2, 13/2=13/2......... b) 84=20x, 20x=84, x=84/20, x=21/5, x=4.2 ver; 12/5=4*4.2/7, 2.4=16.8/7, 2.4=2.4 c) 225=30x, 30x=225, x=225/30, x=15/2, x=7.5 ver; 25/6*7.5=5/9, 25/45=5/9, 5/9=5/9 d) 40x=84, x=84/40, x=21/10, x=2.1 ver; 5/28=3/8*2.1, 5/28=5/28
