Answer:
The probability that the result is positive is P=0.04475=4.475%.
Step-by-step explanation:
We have the events:
D: disease present
ND: disease not present
P: test positive
F: test false
Then, the information we have is:
P(D)=0.005
P(P | D)=0.99
P(P | ND)=0.04
The total amount of positive test are the sum of the positive when the disease is present and the false positives (positive tests when the disease is not present).
The probability that the result is positive is P=0.04475.
Scientific notation is a way to write compactly numbers with lots of digits, either because they're very large (like 2393490000000000000000000), or very small (like 0.0000000000356).
We use powers of ten to describe all those leading/trailing zeros, so that we con concentrate on the significat digits alone.
In your case, the "important" part of the number is composed by the digits 6 and 1, all the other digits are zero. But how many zeroes? Well, let's do the computation.
Every power of 10, is written as one zero followed by n zeroes, so we have
Multiplying a number by means to shift the decimal point to the right and/or add trailing zeroes n times. So, we have to repeat this process six times. We shift the decimal point to the right one position, and then add the five remaning zeroes. The result is thus
