Question 356773
17280(1-10%)^x = 11340
find x
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17280(0.9)^x = 11340
0.9^x = 11340/17280 = 21/32
x*log(0.9) = log(21/32)
x = log(21/32)/log(0.9)
x =~ 3.99783
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The (1 - 10%) is sloppy.  Usually when using per cents, it's specificied to be 10% of something, not just 10%.  This is a poorly written problem, which is why it was ignored for a long time.