In your slider question, click on the "Format" tab.
Under "Slider Settings", you will see "Handle Start Position".
Click on the pull down list and select "Custom". A box will appear. You can enter [%q1_1%] here.
I am assuming your "q1" is also a slider, hence the reason I inserted "q1_1".
You can change this to any previous question and you can also use mathematical calculations on it like [%q1_1*5%] or [%q1_1+10%].