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Concentration of limewater solution

I’m probably committing a schoolboy error here but I’m really really confused.
I’m doing PAG 12.4 to determine the concentration of limewater solution.

The instructions tell me that I am supplied with 250cm3 of limewater that contains 1g dm-3 of calcium hydroxide. Now what confuses me is that surely the instructions just gave me the concentration of the limewater? It literally says it contains 1g mol-3. All I have to do it convert 1g into moles and tadaa? Well it’s obviously wrong but I don’t know why. Also when it asks for the concentration of limewater solution surely by very nature limewater is already a solution of calcium hydroxide and water and they’ve just given me the concentration of that.