[問題]GWD22-19

[magic]

Q19:
Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y. At these rates, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?

A. 4
B. 6
C. 8
D. 10
E. 12
答案是E
請問各位大大這提要怎麼設未知數比較好解題阿??

[Madi]

假設X花a天完成w，Y花a-2天完成w
則每天的工作效率為X:w/a， Y=w/a-2

兩機器工作三天可生產5/4w
因此3(w/a+w/a-2)=5/4w
可求出a=6 or 4/5(因Y=a-2，不合)
所以X需花6*2=12天生產2w

[magic]

謝謝
大大寫的好清楚