Let's make a ratio:
convert percentages to decimals
So, it would take
In real life, the actual mechanics of the sugar dissolving in the water has several variables that may influence the rate of it dissolving. This may become very pronounced if the quantity of water is small in comparison to the quantity of sugar.
Using ratio but in fraction format.
All but 10% means that 90% is dissolved giving:
Multiply both sides by 90