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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?

 Mar 31, 2020
 #1
avatar+423 
+1

Wait what does it mean by half-life? Does it mean that its half of the life span?

 Mar 31, 2020
 #6
avatar+112112 
+1

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

 

 

 

cool cool cool

CPhill  Mar 31, 2020
 #2
avatar+2152 
0

What is the change?

 Mar 31, 2020
 #3
avatar+423 
+1

Hmm if its half wouldnt it live longer?

 Mar 31, 2020
 #4
avatar+112112 
+2

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   

 

 

cool cool cool

 Mar 31, 2020
 #5
avatar+423 
+2

Okay cphill you beat us i guess

 Mar 31, 2020

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