Rb has two isotopes: Rb-85 and Rb-87. If the atomic weight is 85.47 how do I Find the percentages for each?

Question

This is an algabra question in chemistry language. I do not know how to find two unknowns.

Answer 1

You need to know the actual weights of Rb-85 and Rb-87. If you assume that they are 85.00 and 87.00 respectively, then you set the percentage of Rb-85 equal to x, then Rb-87 is 1-x.

85.00 * x + 87.00 (1-x) = 85.47
87.00 - 2x = 85.47
2x = 1.53
x = 0.765
1-x = 0.235

76.5% of the isotopes would be Rb-85, 23.5% would be Rb-87.

Answer 2

McFadden is more likely to be the better RB in the NFL. Bush is not a RB at this level, at least not a complete RB. Bush's position is more about swings and receiving abilities. He has little to no NFL ability to run b/w the tackles or through the line. An incredible talent that was taken WAY too high in the draft (should have been a 3rd rounder) and is being used very inappropriately. McFadden is a much more complete Running Back. If he comes into the NFL and even if he is just mediocre, he'll still be a better RB than Reggie Bush. That's not a slight on Bush, it's a comment towards his talent set being outside of a RBs talent set.

Answer 3

i think you set up the equation this way:

since you know that the average wt is 85.47...

85.47 = 85*x + 87*(1-x) and solve for x then multiply by 100 to get the percentage.

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Answer 4

The first responder has it right. For more accurate answers, use the actual atomic weights: 84.911792 and 86.909186.

Answer 5

Use the force.........I do.