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There are two identical ones in the mall.

In the section on question B mall two identical vending machines sell coffee. The probability that the machine will run out of coffee by the end of the day ... given by the author dry out the best answer is 0.12/0.3=0.4 - the probability that coffee will run out in the second machine.
1-0.12-0.3-0.4 = count yourself. Always consider all options.

Answer from Stretch[guru]
1-0.12 is the probability that coffee will remain either in the 1st machine, or in the 2nd, or in both machines. The problem is solved by the Bayes formula.

Answer from Ludmila Funtova[guru]
Let's consider events. Let

According to the condition P (A) \u003d P (B) \u003d 0.3, P (A B) \u003d 0.12.

NOT
ENDED IN FIRST? DID NOT END IN THE SECOND
NOT
ENDED IN FIRST? ENDED IN THE SECOND

Answer: 0.52

Answer from European[newbie]
320172. There are two identical coffee machines in the mall. The probability that the machine will run out of coffee by the end of the day is 0.3. The probability that both machines will run out of coffee is 0.12. Find the probability that by the end of the day there will be coffee left in both vending machines.
Let's consider events. Let
A - coffee will end in the first machine.
B - coffee will end in the second machine.
Note that events A and B are not incompatible (independent). If they were incompatible, then the probability that coffee ended in both machines would be equal to 0.03 0.03 = 0.09. Then
And V? coffee will run out in both machines,
A+B? at least one machine will run out of coffee.
According to the condition P (A) \u003d P (B) \u003d 0.3 P (A B) \u003d 0.12.
Events A and B are joint, the probability of the sum of two joint events is equal to the sum of the probabilities of these events, reduced by the probability of their product:
P (A + B) \u003d P (A) + P (B) - P (A B) \u003d 0.3 + 0.3 - 0.12 \u003d 0.48.
All event options that can be:

ENDED IN FIRST? DID NOT END IN THE SECOND

ENDED IN FIRST? ENDED IN THE SECOND
The expression “coffee will end in at least one” corresponds to three events from the presented ones. This means that the event “coffee will remain in both machines” is opposite to the event “coffee will end in at least one”. And its probability is 1 - 0.48 = 0.52.

Quest Source: USE 2016 Mathematics, I.V. Yashchenko. Option 5 (tasks 3-5). Solutions. Answer.

Task 3. Find the area of square ABCD. The size of each cell is 1 cm × 1 cm. Give your answer in square centimeters.

Solution.

To solve the problem, we draw a rectangle with a circumscribed rectangle with an orientation equal to the orientation of the cells (red line in the figure).

The area of the circumscribed triangle is square. see The area of the original triangle is less than that described by the amount of equal four right-angled triangles, the hypotenuses of which are equal to the corresponding sides of the original rectangle. The area of each of the triangles is

Then the area of the original rectangle is

Answer: 5.

Task 4. In the mall, two identical vending machines sell tea. The probability that the vending machine will run out of tea by the end of the day is 0.4. The probability that both vending machines will run out of tea is 0.2. Find the probability that by the end of the day there will be tea left in both vending machines.

Solution.

To solve the problem, we introduce two events

The tea will run out in the first vending machine;
- tea will end in the second machine.

The events and are joint, therefore, the probability that tea runs out in at least one machine will correspond to the sum of these probabilities and is equal to

These probabilities are given according to the condition of the problem and are equal to

and

After substituting these values, we get

The probability that tea will remain in both machines is equal to the opposite probability , i.e. the solution to the problem will be

Condition

Two identical vending machines sell coffee in the mall. The probability that the machine will run out of coffee by the end of the day is 0.3. The probability that both machines will run out of coffee is 0.12. Find the probability that by the end of the day there will be coffee left in both vending machines.

Solution

Consider events

By condition

Events $A$ and $B$ are joint, since they can occur simultaneously, therefore, the probability of the sum of two joint events is equal to the sum of the probabilities of these events, reduced by the probability of their product:

Therefore, the probability of the opposite event, that coffee will remain in both machines, is equal to $1-0.48=0.52$ .

Let's give another solution.

The probability that coffee will remain in the first machine is 1 − 0.3 = 0.7. The probability that coffee will remain in the second machine is 1 − 0.3 = 0.7. The probability that coffee will remain in the first or second vending machine is 1 − 0.12 = 0.88. Since $P\left(A+B \right)=P\left(A \right)+P\left(B \right)-P\left(A\cdot B \right)$ , we have: 0.88 = 0.7 + 0.7 - X, whence the desired probability is $x=0.52$.

Note.