Question 1139500

A pot of boiling soup with an internal temperature of 100° Fahrenheit was taken off the stove to cool in a 67°F room. After fifteen minutes, the internal temperature of the soup was 95°F. 

To the nearest minute, how long will it take the soup to cool to 85°F? 
<pre>Using Newton's Law of Cooling - any of the following 3 formulas: {{{highlight_green(system(highlight(matrix(1,3, "T(t)", "=", T[s] + (T[o] - T[s]) * e^(- kt))), OR, highlight(matrix(1,3, dT/dt, "=", - k(T[i] - T[o]))), OR, highlight(matrix(1,3, k(t[1] - t[2]), "=", - ln((T[1] - T[infinity])/(T[2] - T[infinity])))))))}}}, you 
should find that it'll take the soup: {{{highlight_green(matrix(1,5, 55.33465433, or, approximately, 55, minutes))}}} to cool to a temperature of 85<sup>o</sup>F.