[Sophia7X]

I've been trying to figure out this for days... Any help, please?
I'm not sure how to use the a+b to the n power formula they give you. Answer is supposed to be 0.77.

All help appreciated. Thanks.

[Sophia7X]

Never mind; don't answer this, I got it.

[sjb]

Never mind; don't answer this, I got it.

Care to share, to help others who may pass this way in the future?

[Sophia7X]

Never mind; don't answer this, I got it.

Care to share, to help others who may pass this way in the future?

Yes of course.
It turned out that this was just a math problem, essentially. The (a+b)ⁿ they gave you is supposed to be expanded with binomial theorem. So (a+b)⁴= a⁴ + 4a³b + 6a²b² + 4ab³ + b⁴

Only the first term and second term matter (M and M+2) because the light isotope's mass is 35 and heavy Cl isotope is 37.

You plug in the relative abundance into a⁴ and 4a³b (a=0.7577 and b=0.2423), take the ratio and get ~0.78.