Hello!
The graph, (2/5)^x is an exponential function.
Since there is not a negative symbol in the front of the function, options A and B are incorrect.
For option 3 to be correct, there would need to be a negative symbol in front of the exponent, x.
So therefore, the answer option 4. (Also, I'll post a graph. :))
The balloon has a volume dependent on its radius
:
Differentiating with respect to time gives
If the volume is increasing at a rate of 10 cubic m/s, then at the moment the radius is 3 m, it is increasing at a rate of
The surface area of the balloon is
and differentiating gives
so that at the moment the radius is 3 m, its area is increasing at a rate of