On a calculator keypad, there are the numbers from 0 to 9 and signs of two actions (see the figure). First, the display shows the number 0. You can press any keys. The calculator performs the actions in the sequence of clicks. If the action sign is pressed several times, the calculator will only remember the last click.
a) The button with the multiplier sign breaks and does not work. The Scattered Scientist pressed several buttons in a random sequence. Which result of the resulting sequence of actions is more likely: an even number or an odd number?
b) Solve the previous problem if the multiplication symbol button is repaired.
On a Christmas tree, 100 light bulbs hang in a row. Then the light bulbs begin to switch according to the following algorithm: all are lit up, then after a second, every second light goes out, after another second, every third light bulb changes: if it was on, it goes out and vice versa. After another second, every fourth bulb switches, a second later – every fifth and so on. After 100 seconds the sequence ends. Find the probability that a light bulb straight after a randomly selected light bulb is on (bulbs do not burn out and do not break).
In the final of a contest of performances on March 8 two performances were left. In the first, \(n\) pupils from the class 5A performed, and in the second – \(n\) pupils of class 5B. At the play there were \(2n\) mothers of all \(2n\) students. The best performance is chosen by a vote by the mums. It is known that every mother, with a probability of \(\frac 12\), votes for the best performance and with a probability of \(\frac 12\) – for the performance in which her child participates.
a) Find the probability that the best performance will win with a majority of votes.
b) The same question, if more than two classes have reached the finals.
In honor of the March 8 holiday, a competition of performances was organized. Two performances reached the final. \(N\) students of the 5th grade played in the first one and \(n\) students of the 4th grade played in the second one. The performance was attended by \(2n\) mothers of all \(2n\) students. The best performance is chosen by a vote of the mothers. It is known that half of the mothers vote honestly, i.e. for the performance that was truly better and the mothers of the other half in any case vote for the performance in which their child participates.
a) Find the probability of the best performance winning by a majority of votes.
b) The same question but this time more than two performances made it to the final.
A sailor can only serve on a submarine if their height does not exceed 168 cm. There are four teams \(A\), \(B\), \(C\) and \(D\). All sailors in these teams want to serve on a submarine and have been rigorously selected. There remains the last selection round – for height.
In team \(A\), the average height of sailors is 166 cm.
In team \(B\), the median height of the sailors is 167 cm.
In team \(C\), the tallest sailor has a height of 169 cm.
In team \(D\), the mode of the height of the sailors is 167 cm.
In which team, can at least half of the sailors definitely serve on the submarine?
The length of the hypotenuse of a right-angled triangle is 3.
a) The Scattered Scientist calculated the dispersion of the lengths of the sides of this triangle and found that it equals 2. Was he wrong in the calculations?
b) What is the smallest standard deviation of the sides that a rectangular triangle can have? What are the lengths of its sides, adjacent to the right angle?
The upper side of a piece of square paper is white, and the lower one is red. In the square, a point F is randomly chosen. Then the square is bent so that one randomly selected vertex overlaps the point F. Find the mathematical expectation of the number of sides of the red polygon that appears.
In a numerical set there is 100 numbers. If you remove one number, the median of the remaining numbers will be 78. If you remove a different number, the median of the remaining numbers is 66. Find the median of the entire set.
In the city where the Scattered Scientist lives, telephone numbers consist of 7 digits. The scientist easily remembers a phone number, if this number is a palindrome, that is, it is identical when read from left to right and from right to left. For example, the number 4435344 the scientist remembers easily, because this number is a palindrome. And the number 3723627 is not a palindrome, so the scientist does not remember this number easily. Find the probability that the scientist will remember the phone number of a new random acquaintance easily.
Ben is going to bend a square sheet of paper \(ABCD\). Ben calls the fold beautiful, if the side \(AB\) crosses the side \(CD\) and the four resulting rectangular triangles are equal. Before that, Jack selects a random point on the sheet \(F\). Find the probability that Ben will be able to make a beautiful fold through the point \(F\).