If the average (arithmetic mean) of x and y is 40, and z-x=60, what is the avera

游客2024-01-14  10

问题 If the average (arithmetic mean) of x and y is 40, and z-x=60, what is the average of y and z?

选项 A、20
B、50
C、65
D、70
E、140

答案 D

解析 To get the average of y and z, you need to find half of the sum of y+ z. To obtain that number, first restate the first statement as an equation: x+y=80. Add that equation to z-x=60, so that x+y+z-x=80+60=y+z=140. The average of y and z is 140/2=70.
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