Add.
(3x4 – 2x3 + 1) + (12x4 + x2 – 11)
answer
15x4 – 2x3 + x2 + 10
15x4 – x3 – 10
15x4 – x2 – 10
15x4 – 2x3 + x2 – 10

Here is how you are going to add the given polynomials:
3x^4     - 2x^3              -11
12x^4              +x^2     +1    <<< Add these using the normal addition process

15x^4 - 2x^3  +x^2 -10
Therefore, the answer would be the last option: 15x4 – 2x3 + x2 – 10
Hope this is the answer that you are looking for. Thanks for posting!

a) What is the probability that the duration of a particular rainfall event at this location is at least 2 hours?

We want this probability"

At most 3 hours?

b) What is the probability that rainfall duration exceeds the mean value by more than 2 standard deviations?

What is the probability that it is less than the mean value by more than one standard deviation?

Step-by-step explanation:

Previous concepts

The exponential distribution is "the probability distribution of the time between events in a Poisson process (a process in which events occur continuously and independently at a constant average rate). It is a particular case of the gamma distribution". The probability density function is given by:

The cumulative distribution for this function is given by:

We know the value for the mean on this case we have that :

Solution to the problem

Part a

What is the probability that the duration of a particular rainfall event at this location is at least 2 hours?

We want this probability"

At most 3 hours?

Part b

What is the probability that rainfall duration exceeds the mean value by more than 2 standard deviations?

The variance for the esponential distribution is given by:

And the deviation would be:

And the mean is given by

Two deviations correspond to 5.540, so we want this probability:

What is the probability that it is less than the mean value by more than one standard deviation?

For this case we want this probablity: