1. Let the total number be 1, 1/2 = 1/2,1/2×1/3 =1/6,65438+. 1-2/3-115 = 4/15,60 ÷ 4/15 = 225 I don't understand the second question. What's the total number of three people ... 3. Let's set the attendance X and the leave Y, so we must be 4. Let the first bag X and the second bag Y, x+ 15=y, 1/3x=2/7y, so that x is 90 and y is 105.