how do we calculate the percentage abundance of any element??/
Kindly refer to the similar link given below :
https://www.meritnation.com/ask-answer/question/the-average-atomic-mass-of-two-isotopes-with-mass-numbers-a/structure-of-the-atom/10351059
https://www.meritnation.com/ask-answer/question/the-average-atomic-mass-of-two-isotopes-with-mass-numbers-a/structure-of-the-atom/10351059