Chemistry problem about concentration

10.0mL of a 1.0M solution is diluted to 250.0mL. What is the concentration of the diluted solution?

the answer i got was 0.04M, but i'm not sure if it's right. can someone explain how to do this kind of problem?

Here's a nice change of pace. You've actually attempted the problem. Great!

There's an app for that:
C1 x V1 = C2 x V2 .... where C represents concentration and V is volume.
Solve for C2
C2 = C1V1/V2
C2 = 1.0M x 10.0 mL / 250.0 mL = 0.0400 M

This is based on the notion that the original moles of the solute will be the same regardless of how much solvent has been added. Think of how you compute molarity:

molarity = moles of solute / liters of solution
Moles = molarity in moles / liters x liters of solution
and that is where C1 x V1 comes from

First, find the number of particles in the original solution.

1.0M= (xmols/.01L), solving for x tells you that you have .01 mol.

Now do .01mol/.250L= x. The answer is .04M.

M1V1 = M2V2 [1, 2 should be subscript]
M = molarity ; V = volume

So, 1 M * 10 mL = M2 * 250 mL

M2 = 10/250 = 0.04 M

You got it right :)