Question

At the moment a hot iron rod is plunged into freezing water, the difference between the rod's and the water's temperatures is 100\degree100°100, degree Celsius. This causes the iron to cool and the temperature difference drops by 60\%60%60, percent every second.

Which graph shows the temperature difference yyy (degrees Celsius) after xxx seconds?

Answer 1

D(t)=100(0.4)^t

Explanation:

Answer 2

The function is
`D(t) = 100 *( (40)/(100) )^(t)`.

Step-by-step explanation:

At t = 0 the difference is 100 degree celsius.

After one second the temperature difference will be
`100 - (100*60)/(100) = 100(1 - (60)/(100) )`

After two second, the difference will be
`100(1 - (60)/(100) )(1 - (60)/(100) ) = 100(1 - (60)/(100) )^(2)`

Hence, it can be written that,

D(t) =
`100 *(1 - (60)/(100) )^(t) = 100 *( (40)/(100) )^(t)`