The 2 equations are
18.20x+19.50y=230.10
and
x+y=12
where x is the months of original cost and y is months for new cost. Since you know that you paid for one year (12 months) you can make the second equation. Then you want to substitute the first equations x by making the second equation
x=(12-y)
18.20(12-y)+19.50y=230.10
218.40-18.20y+19.50y=230.10
1.30y=11.70
y=9
so that means you had the original rate for 3 months and the new one for 9 months
Each complete cleaning requires 6 drops of cleaner. Let's convert that to ml:
6 drops 1 ml 3 ml cleaner
----------- * ------------- = ------------------- = 0.3 ml cleaner per cleaning
20 drops 10 cleanings
Recall that 1 bottle contains 30 ml cleaning fluid.
How many cleanings is one bottle of fluid good for?
1 bottle 0.3 ml
----------- = ----------- => x = 100 cleanings/bottle
x 30 ml
Answer: 
Step-by-step explanation:
Binomial probability formula :-
, where P(x) is the probability of getting success in x trials, n is the total number of trials and p is the probability of getting success in each trial.
We assume that the total number of days in a particular year are 365.
Then , the probability for each employee to have birthday on a certain day :
Given : The number of employee in the company = n
Then, the probability there is at least one day in a year when nobody has a birthday is given by :-
Hence, the probability there is at least one day in a year when nobody has a birthday =
