Referring to the methods for calculating average atomic mass, which one is 'incorrect' ? Mary
Jack
Alan

I think Mary's and Alan's Methods are wrong. Jack is correct.  

Explanation:

(M1)(%)+(M2)(%)+(M3)(%)

You will be mulitplying the mass of Isotopes  by the percentages, (M1,2,3) are the isotopes. Then you just add the three to get the average.

There isn't any division involved.

i just calculated it all out, and not including weekends, and all the different days off. as of this school year (2018-2019) students are spending 2198 hours in school this year

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.