Fred's final mark in an online course was determined entirely by two exams.The mid-term exam was out of x marks and was worth 25% fo his final mark.The final exam was out of 2x marks and was worth 75% of his final mark.Fred scored 40 marks on the first exam and 60 marks on the second exam.Determine the value of x if Fred earned a final mark of 50% in the course.
问题描述：
Fred's final mark in an online course was determined entirely by two exams.The mid-term exam was out of x marks and was worth 25% fo his final mark.The final exam was out of 2x marks and was worth 75% of his final mark.Fred scored 40 marks on the first exam and 60 marks on the second exam.Determine the value of x if Fred earned a final mark of 50% in the course.
答
(40/x)·0.25+(60/2x)·0.75=50%
解x就可以了
答
由题,可列方程
(40/x) ×0.25 + [60/(2x)]×0.75 =0.5
即,(10/x) + (22.5/x) =0.5
32.5/x =0.5
解得,x=32.5/0.5=65
so,the value of x is 65