or
If the unit after adding water for the first time is 1, there will be 3% sugar and 2% sugar for the second time.
Then add 3%/2% water-1 = 0.5, then the third total * * is 1+0.5+0.5=2.
So the concentration is 3%/2= 1.5%.
or
Assuming that the total mass of sugar water is 100g and the concentration is 3% after adding water for the first time, the sugar is 3g and the water is 97g.
After adding x grams of water for the second time, the concentration became 3÷( 100+X)=2%, and the solution was x = 50g.
At this time, the total mass of sugar water is 150g.
After adding 50g of water for the third time, the concentration became 3÷( 150+50)= 1.5%.
I said three, do you understand?