# Gallium has two naturally occurring isotopes. The mass of gallium-69 is 68.9256 amu and it is 60.108% abundant. The mass of gallium-71 is 70.9247 amu and it is 39.892% abundant. What is the atomic mass of gallium?

##### 1 Answer

#### Explanation:

To find the average **atomic mass** (**that is expressed as a decimal** and total the results. We can carry this out in a single line of working:

Similarly, you could input the percentages normally and then divide by

Notice that the answers are the same. Also observe that the answer is closer to 69 than it is to 71, which makes sense since gallium-69 makes up a greater proportion of gallium in the universe (