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The first pile has the same number of black and white pieces as the second pile. The third pile accounts for 40% of the total black pieces, and the white ones account for a few parts of the total There should be a formula
Suppose there are x pieces in each pile. If the first pile has y black pieces, then the second pile has y white pieces
One pile of sunspots is X-Y. two piles of sunspots are X-Y. one or two piles of sunspots have y + X-Y
All sunspots are x / (1-0.4) and white ones are 3x-5x / 3 = 4x / 3
So the percentage of Baizi is 4x / 3 / 3x = 4 / 9
There are three piles of chessmen, with the same number and only black and white. The first pile has the same number of black and white as the second pile, and the third pile has the same number of white
————There are as many sunspots in the first pile as in the second——————
The third pile of white children accounts for three seventh of all white children
How many pieces do sunspots occupy
5/12.
Let the total number of chess pieces be x and the total number of white pieces be y
Then: the value is (X-Y) / X
Conditions: there are as many sunspots in the first pile as in the second pile
Let the first set of white numbers Y1 and the second set Y2
y1=x/3-y2.
The third pile of white children accounts for three seventh of all white children
Let Y3 be the third white number
y3=3/7y.
In addition: Y1 + Y2 + Y3 = y
The solution is: x = 12 / 7Y
So: (X-Y) / x = 5 / 12
Red, yellow and green glass balls. After many tests, the frequency of red, yellow and green balls is 25%, 45% and 30% respectively. It is estimated how many red and yellow balls are in the bag
Green ball
How many glass balls are there in this pile? Suppose yellow balls: X red balls: (28 + x). Green balls: 2x, because green balls are twice as many as yellow balls, that is: 2x = x + 18 + 18, x = 36, that is, yellow balls 36
There is a box of glass balls in red, yellow and green, and the number is close to 400. Among them, red glass balls account for 14% of the total, yellow glass balls account for N9% of the total. The number of green glass balls is not the most or the least. How many red, yellow and green glass balls are there?
Because the number of balls is a multiple of 4 and 9 and close to 400, the total number of balls is 396. Then red balls: 360 × 14 = 99, yellow balls: 396 × N9 = 44N; then green balls: 396-99-44n = 297-44n, because the number of green glass balls is not the most or the least, so: the first case: 297-44n > 99
There are 72 red, blue and white glass balls of the same size, which are always arranged in the order of 2 red balls, 3 blue balls and 4 white balls
It's 72
With glass ball: 72 / (2 + 3 + 4) = 8 (Group)
Blue glass balls account for 3 * 8 / 72 = 1 / 3 of the total
There are 76 red, blue and white glasses of the same size, which are always arranged in the order of 2 red balls, 3 blue balls and 4 white balls
How many of the three kinds of glass balls account for? What color is the 50th glass ball?
According to the order of 2 red balls, 3 blue balls and 4 white balls, each group has 9 balls, 8 × 9 = 72;
In the end, there were four, two red balls, two basketballs, and one basketball;
Therefore, among the 76 red balls, 2 × 8 + 2 = 18, accounting for 18 / 76 = 9 / 38;
Basketball: 3 × 8 + 2 = 26, accounting for 26 / 76 = 13 / 38;
White ball: 4 * 8 = 32, accounting for 32 / 76 = 819;
5 × 9 = 45, so the remaining five are basketball;
The 50th is basketball
There are 72 red, blue and white glass balls of the same size. There are always 2 red balls, 3 basketball balls and 4 white balls in the order. How many points does basketball occupy in the total number
One third
There are 56 red, blue and white balls of the same size, arranged in the order of 2 red balls, 3 blue balls and 4 white balls
What percentage of the total
56 △ 2 + 3 + 4 = 56 △ 9 = 6, the remaining 2 (this 2 is two red balls)
Therefore, the number of basketball is 3 * 6 = 18
The proportion of basketball is 18 / 56 = 9 / 28
There are 20 balls in a box, including 10 red balls, 6 white balls, 4 yellow balls, 4 random balls, and the probability of at least three red balls
But because I didn't learn permutation and combination, I can't calculate the probability of taking four out of ten red balls. Why is 210? The answers on the 2nd, 3rd and 4th floor are all right, but can you tell me about combination first?
3Q~
Answer: 94 / 323
Analysis: at least three red balls have two situations
1. Three red balls. Three out of ten * one out of ten / four out of twenty = 80 / 323;
2. Four red balls. Four out of ten / four out of twenty = 14 / 323
It adds up to 94 / 323
(I can't type the symbols of permutation and combination. You can understand them yourself.)
Supplement:
1. The calculation rule of permutation and combination is as follows:
The combination of 4 out of 20 = 20 * 19 * 18 * 17 / 4 * 3 * 2 * 1; the combination of 3 out of 10 = 10 * 9 * 8 / 3 * 2 * 1;
N combinations in M = m * (m-1) * (m-2) * ·· * (m-n + 1) / N * (n-1) * (n-2) * ·· * 1
4 out of 20 = 20 * 19 * 18 * 17; 3 out of 10 = 10 * 9 * 8;
The permutation of N in M = m * (m-1) * (m-2) * ·· * (m-n + 1)
2. The difference between permutation and combination is that the objects of permutation should consider the order, while the combination does not consider the order of groups. For example, we do not need to consider which ball is selected first and which ball is selected later, so we use combination. If the problem is to select four balls from 20 different balls and put them into four different boxes a, B, C and D respectively, We have to arrange them, because we have to not only choose four balls, but also consider which box to put
The ability of expression is limited. I don't know if you can understand it. If you can't understand it, look for a book
There are four red balls, two white balls, one yellow ball and several blue balls in the bag. How many blue balls are there if the probability of touching the blue ball is 0.3
zenme
qiu
By convention
Your touch means one touch and one touch
There are 7 non basketball players in total, so suppose there are x basketball players
That's X / (x + 7) = 0.3
Three blue balls can be obtained by solving the equation
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