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Help with a question

I’m stuck on this question could someone please explain it, and give me an answer? Thank you!DFCA9073-C1DE-4F21-B308-1E9129604454.jpg.jpeg
question a
60+40=100
60/100=60% composition of 69Ga
40/100=40% composition of 71Ga

question b
((40x71)/100)+((60x69)/100)=69.8=the relative atomic mass
Reply 2
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Macdeff
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13
Thank you so much!! Could you please help me with one more question?
Reply 3
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Macdeff
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13
E4DAC0F0-E35D-4DF9-884B-4930E6E603FA.jpg.jpeg
((79x)+(81(100-x))/100=79.9

79x + 81(100-x)=7990

79x +8100 - 81x = 7990
2x=110
x=55

percentage of 79Br is 55%
percentage of 81Br is 45% (100-55)

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