Answer
In order to use the distributive property I first get the amount of the water fell in ;
One year
1.68mm
A half a year
½× 1.68mm
= 0.84mm
One and a half years (Using the distributive property)
1.68mm + 0.84mm
168mm + 84mm
100. 100
(168÷100) + (84÷100)
(168+84) ÷ 100
252 ÷ 100
252
100
= 2.52mm
Therefore the variation in the water level in the time period was 2.25mm