Найдите сумму 1/2+1/3+1/5 1/2+1/5+3/7 1/2+2/3+3/5 2/3+1/4+1/5

Чтоб найти сумму приведем дроби к общему знаменателю:

1) 1/2 + 1/3 + 1/5 = (1 * 15)/(2 * 15) + (1 * 10)/(3 * 10) + (1 * 6)/(5 * 6) = 15/30 + 10/30 + 6/30 = (15 + 10 + 6)/30 = (25 + 6)/30 = 31/30 = 1 1/30;

2) 1/2 + 1/5 + 3/7 = (1 * 35)/70 + (1 * 14)/70 + (3 * 10)/70 = 35/70 + 14/70 + 30/70 = (35 + 14 + 30)/70 = (65 + 14)/70 = 79/70 = 1 9/70;

3) 1/2 + 2/3 + 3/5 = (1 * 15)/30 + (2 * 10)/30 + (3 * 6)/30 = 15/30 + 20/30 + 18/30 = (15 + 20 + 18)/30 = (35 + 18)/30 = 53/30 = 1 23/30;

4) 2/3 + 1/4 + 1/5 = (2 * 20)/60 + (1 * 15)/60 + (1 * 12)/60 = 40/60 + 15/60 + 12/60 = (40 + 15 + 12)/60 = (55 + 12)/60 = 67/60 = 1 7/60.