How many argon molecules have velocities between 250 m/s and 500 m/s?

[baubletop]

Homework Statement

A sealed bottle at 1 atm of pressure holds 1 mole of neon and 1 mole of argon gas at a temperature of 295K. The curves in the Figure (http://phlnx3.pas.rochester.edu/webwork2_files/CAPA_Graphics/Gtype43/prob01a.gif) show the distributions of velocities of the molecules of each gas.
Find the number of molecules of argon which have velocities between 250 m/s and 500 m/s.

Homework Equations

KE = (3/2)kT
P(v) dv $\propto$ 4πv^2 e^((-(1/2)mv^2)/kT) dv
Molar Mass of Argon = 0.03995 kg/mol

The Attempt at a Solution

Totally lost on how to set this one up. I get that I need some sort of bound on the probability of finding Argon between 250 and 500 m/s, and from there I can get an actual number, but for now I'm somewhat lost.
The graph might be giving me the answer right in front of me but I'm also having a hard time reading it (it doesn't help that it's not labeled which curve is which element...).

 

[Chestermiller]

Argon has a higher molar mass than neon. What does that tell you about which curve is which? As a last resort, you can count area under the curve from 250 to 500.

 

[baubletop]

It should be the top curve since vrms would be lower than Neon. I thought it would be harder than that but I just manually calculated the area and got the right answer. Guess I was overthinking it. Thanks!