这条水渠全长 x 米.
(x-500)/500 = 5/3
==> 3(x-500) = 500 * 5
==> 3x - 1500 = 2500
==> 3x = 4000
==> x = 4000/3 (米)
列式计算：500 / [1 / (5/3 + 1)] = 500 / (3/8) = 500 * 8 /3 = 4000/3 (米)4000/3什么意思