甲数是乙数、丙数、丁数之和的2分之1，乙数是甲、丁、丙之和的3分之1，丙数是甲数、乙数丁数之和的4

260÷(1- (1/2)/(1+1/2)- (1/3)/(1+1/3)- (1/4)/(1+1/4)) =260÷(1-1/3-1/4-1/5) =260×60/13 =1200