Сравни148+150 и 249111 и 221+123(1225) и (12)(25)(1225) и

1) (1/48+1/50)   gt;  2/49
НОЗ (48,49,50)=48*49*25=58800
48= 6*8= 2*2*2*2*3
49=7*7
50=5*10=2*5*5
1/48+1/50 = (1*25*49 + 1*24*49)/ 58800= (1225+1176)/58800=2401/58800
2/49 = (2*48*25)/ 58800 = 2400/58800
2401 / 58800  gt;  2400/5880
2) 1/11  lt;    2/21+1/23
НОЗ ( 11,21,23) =  11*21*23= 5313
2/21 + 1/23= 506/5313+ 231/5313= 737/5313
1/11= 483/5313
483/5313 lt; 737/5313
3) (1/2+2/5) gt;  (1/2) х (2/5)
(1/2 х 2/5) = ( 5)= 25
(1/2) х (2/5) = 1/4 х 4/25 = 1/25 
25 gt; 1/25
4)  (1/2 : 2/5)   =  (1/2): (2/5)
(1/2 : 2/5)  = ( 1/2 х 5/2) = (5/4)= 25/16 = 1 9/16
(1/2) : (2/5) = 1/4 :  4/25 = 1/4 х 25/4 = 25/16= 1 9/16