Calcium has three different isotopes. One has a mass of 35.00 amu; another has a mass of 41.00 amu; the third has a mass of 40.00 amu. Which isotope is most abundant of the three? How do you know?
I want to say it is the isotope with the largest atomic mass unit, but there are no percentages so I don't know of a way to be sure which one could be more abundant.