Question 1187549
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Suppose that someone made a hot pizza, right after taking it out of the oven it had the temperature of 110C°, 
we can only ingest it, without the risk of it burning us, when it have its temperature equivalent to 40°C. 
The temperature of the food decreases according to the function: f(t)= 120.2^( - 1.6t)+10, with t being minutes. 
Once ready, from how long can we ingest it without the risk of getting burned?
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Write the equation as you read the problem


    120*2^(-1.6t) + 10 = 40   degrees of Celsium


Simplify it step by step


    120*2^(-1.6t) = 40 - 10

    120*2^(-1.6t) =    30

    2^(-1.6t)     =    30/120

    2^(-1.6t)     =    1/4

    2^(-1.6t)     =    2^(-2)


Since the exponents are equal and the bases are equal, we conclude that the degrees/(indexes) are equal


       -1.6t      =     -2        

           t      =     {{{(-2)/(-1.6)}}} = {{{2/1.6}}} = 1.25 

<U>ANSWER</U>.  The customer should wait 1.25 minutes = 1 minute and 15 seconds.
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Solved.