Im having trouble understanding this problem so if you can s

I\'m having trouble understanding this problem so if you can show how you figured out the answer step by step that would be great! thank you :))

Solution

The meteorite has radioactive potassium-40 and argon-40. The potassium decays into argon in about 1.25 billion years. The remains of potassium on the rock are only 8.5% of its original value. By the hint given we can assume that the rock was originally 100% potassium and now there is only 8.5% of its value. That means 91.5% of those years has passed.

100% -> 1.25bill

91.5% -> x

X= (91.5% * 1.25bill) / (100%)

x= 1.14375 billion years( how old the rock is).