Question

calculate the average atomic mass of an element it has 2 isotopes 79÷35 × (49.7%) and 81÷35 × (50.3%)
Please answer and step by step

Answer 1

average atomic mass =
79×497 /1000+81×503/1000
39.263+ 40.743
80.006
80u

Answer 2

Answer:

Let the number be x, so that

x × 9/10 = 81

or, x = 81 × 10/9 = 9 × 10 = 90

So, that number is 90.

To Check :-

90 × 9/10 = 81

or, 9 × 9 = 81

or, 81 = 81

LHS = RHS

Hence, Verified.

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