Three isotopes of Neon occur naturally:

20Ne (mass = 19.9924 amu)
21Ne (mass = 20.9938 amu)
22Ne (mass = 21.9914 amu)

If the percent abundance of 21Ne is 0.2600, what is the percent abundance of 20Ne?

How do I set up for these type of problems. I tried just using two and realized that was wrong. I can't use (1-x) or x since I have more than what isotope so what do I do?

How about this?

20Ne + 21Ne + 22Ne = 100%
20Ne + 0.26 + 22Ne = 100% and
20Ne + 22Ne = 100-0.26 = 99.74%
Let x = 20Ne and 0.9974-x = 22Ne
Set your equation up as usual and solve for x and 0.9974-x.

ahh thank you so much!

To solve this problem, you can use the concept of percent abundance. Percent abundance represents the percentage of a particular isotope in a sample of an element.

Here's how you can set up the problem step-by-step:

1. Assign variables for the percent abundances of the isotopes. Let x represent the percent abundance of 20Ne, and 0.2600 represents the percent abundance of 21Ne.

2. Since the sum of the percent abundances of all isotopes should equal 100%, you can express the percent abundance of 22Ne as (100% - x - 0.2600%).

3. Convert the percent abundances to decimal form, so x becomes x/100 and 0.2600 becomes 0.2600/100.

4. Set up an equation using the atomic masses and the percent abundances for the total mass of neon:
(20Ne atomic mass) * (x/100) + (21Ne atomic mass) * (0.2600/100) + (22Ne atomic mass) * ((100% - x - 0.2600)/100) = total mass

5. Substituting the atomic masses:
(19.9924 amu) * (x/100) + (20.9938 amu) * (0.2600/100) + (21.9914 amu) * ((100% - x - 0.2600)/100) = total mass

Now, you can solve this equation for x, representing the percent abundance of 20Ne. By rearranging and simplifying the equation, you'll find the value of x, which will be the percent abundance of 20Ne.