# Physics HELP HELP

(for some reason I keep getting this wrong. I put 90 for c, 5.6 for h and 22 for M(x), Then I took the natural log of both sides, but I keep getting it wrong)

The mass of a radioactive element at time x is given by the equation below, where c is the original mass and h is the half-life of the element. The half-life of a substance is 5.6 years. How long will it take for 90 grams to decay to 22 grams? (Round your answer to one decimal place.)
M(x) = c (.5^{x/h})

1. 22=90 (1/2)^t/5.6

22/90=1/2^t/5.6
log (22/90)= t/5.6 log .5
t= 5.6 log (22/90)/log .5

log (22/90)=-.6118
log .5= -.3010
I am uncertain what you did.

posted by bobpursley

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