2019年新加坡的塑料垃圾量为 900 000 吨。
这比2018年增加了 10%。
求2018年的塑料垃圾量。 答 ___ 吨

1. Represent the 2019 amount as a percentage of the 2018 amount.

Since 2019 is an increase of $10\%$ from 2018,

$2019\text{ amount} = 110\% \text{ of 2018 amount}$

2. Divide by 110% to find the original 2018 amount.

Let the 2018 amount be $x$ tonnes.

$1.10x = 900\,000$

$x = \frac{900\,000}{1.10} = 818\,181.818\ldots$

So the amount of plastic waste in 2018 was approximately $818\,182$ tonnes.