helena312 1) 3/7 и 2/5
3/7= (3*5)/7*5=15/35
 2/5= (2*7)/5*7=14/35
2) 5/12 и 7/16
  5/12=(5*4)/12*4=20/48  
 7/16=(7*3)/16*3=21/48
3) 13/60 и 7/15    
13/60  
7/15= (7*4)/15*4=28/60
4) 7/20 и 11/30
   7/20=(7*3)/20*3=21/60  
11/30=(11*2)/30*2=22/60

петя009 1.  3\7 и 2\5 = 14\35 и 15\35   2. 5/12 и 7/16 = 80/192 и 84/192   3.  13/60 и 7/15 = 420/900 и 195/900    4. 7/20 и 11/30 = 210/600 и 220/600