chemistry help!
posted by Skylar .
Potassium has an atomic mass of 39.10amu. a sample of potassium is made up of isotopes potassium39 (mass=38.964) and potassium41(mass =40.962 amu). What percentage of the potassium sample is potassium39? what percent of the sample is potassium41?

For a sample of K, with x grams of ^{39}K and y grams of ^{41}K the total mass will be
38.964x + 40.962y
Assuming a sample of 100g, we have
38.964x + 40.962(100x) = 39.10(100)
x = 93.193
^{39}K is 93.193%
^{41}K = 6.807%
check:
38.964*.93193 + 40.962*.06807 = 39.10