Itâ€™s a probability question. The probability of getting this certain combination of isotopes to add up to a total of 128 in the compound. I did the calculation for you down below. Let me know if you have any questions about that.

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heyy thanks for the solution, may i ask where did you get the 3/4 and 1/2 that you multiplied?

its in the question: â€śChlorine 35 is three times more common (=3/4) than chlorine 37 (=1/4)â€ť and â€śBromine 79 is present in equal numbers as bromine 81 (both= 1/2)â€ť

The fractions tell you what proportion of the element has a certain mass number.

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Darius is correct! :))

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thanks!! that explains a lot

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