某化學工廠之廢水為Hg2+的重量百分率為0.0003%

1 ppm = 1 x 10⁻⁶

此廢水之Hg²⁺含量
= 0.0003%
= 0.0003% x (1 x 10⁶) x (1 x 10⁻⁶)
= 3 x 10⁻⁶
= 3 ppm


若不用科學記數法：
1 ppm = 1/1000000

此廢水之Hg²⁺含量
= 0.0003%
= 0.0003% x (1000000/1000000)
= 3/1000000
= 3 ppm

可以去請教化學老師~~~