Help with Fluid Statics and Dynamics?

So I need help with the relationship between velocity and the radius of a pipe. If a pipe had a radius that decreased by 1/2 its original size, then does the velocity increase by two? I had that as my answer for a test, but it was marked wrong. Here's one of the questions relating to my problem: An ideal... show more So I need help with the relationship between velocity and the radius of a pipe.
If a pipe had a radius that decreased by 1/2 its original size, then does the velocity increase by two? I had that as my answer for a test, but it was marked wrong.
Here's one of the questions relating to my problem:

An ideal fluid flows through a long horizontal circular pipe. In one region of the pipe, it has a radius R. the pipe then widens to radius 2R. What is the ratio of the fluid's speed in the region of radius R to the speed of the fluid in region 2R?

I stated 2V, but I was wrong there as well. The only other increasing measurement was 4V, since the velocity couldn't decrease since the pressure was increasing. If it is 4, then how do you get to that conclusion?
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