猎人带狗追捕，兔子刚跑80步，猎狗去追兔子，已知猎狗跑2步的时间兔子跑3步，猎狗跑4步的距离与兔子跑7步的距离相等。那么猎狗跑多少步可以捕获这只兔子？
距离80步
2a/x = 3b/y
-> 2ay = 3bx
-> x = 2ay/3b
4*a = 7*b
->a = 7b/4
带入x = 2ay/3b
x = 2*7by/12b
x = 7y/6
b = 4a/7
(n*a - 80*b)/y = n*a/x
n*a*x - 80*b*x = n*a*y
n*a*(x-y) = 80*b*x
n = 80*b*x
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a*(x-y)
= 80 *4a/7* 7y/6
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a* (7y/6 - y)
= 80*4/7 *7y/6
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1y/6
= 80*4=320