The half-life of a radioactive substance is 245 days. How long will it take for 79 grams of the substance to decay to 43 grams?
Wait what does it mean by half-life? Does it mean that its half of the life span?
The half-life of a substance is the time it takes for the substance to decompose to 1/2 of its original amount
In the case....it takes 245 days to decompose to 79/2 = 39.5 g
What is the change?
Hmm if its half wouldnt it live longer?
We have that
43 = 79 * (1/2)^(t / 245 ) divide both sides by 79
(43/79) = (1/2)^( t / 245) take the log of both sides
log ( 43/79) = log (1/2)^(t/245) and we can write
log ( 43/79) = (t / 245) log (1/2)
245 log (43/79) / log (1/2) = t ≈ 215 days
Okay cphill you beat us i guess
+422 
