A box of beads, the first time out of the total number of 15 and 4, the second time out of the remaining 14 and 3, the third time out of the remaining 13 and 2, the fourth time out of the remaining 12 and 1, then there is still one in the box. How many original beads in the box?

Starting from the last remaining one, push forward, take away the third time, the remaining one is (1 + 1) × 2 = 4, the second time is: (4 + 2) / (1-13) = 6 / 23 = 9, the first time is: (9 + 3) / (1-14) = 12 / 34 = 16, so this box of beads has (16 + 4) /

Tiantian arranges 25 beads into five piles with different numbers. The number of beads in each pile is odd. Do you know how many beads there are in each pile?

1. 3, 5, 7, 9

There are three piles of black-and-white chessmen, each pile of chessmen is 30. There are as many sunspots in the first pile as in the second pile, and the sunspots in the third pile account for 4% of all the sunspots
No equations!
One in four

The third pile of sunspots accounts for 1 / 4 of all sunspots, which means that the ratio of the sum of the first two piles of sunspots is 1:3. The first pile of sunspots plus the second pile of sunspots is 30 (because there are as many sunspots in the first pile as the second pile of white ones), so the third pile of sunspots is 30 * (1 / 3) = 10

There are three piles of chessmen, each pile has the same number of chessmen, and only has black and white chessmen. The first pile has the same number of black chessmen as the second pile, and the third pile has 1 / 4 of all the black chessmen. Put these three piles of chessmen together, and how many parts of the total number of white chessmen account for

Exchange the first pile of sunspots with the second pile of sunspots to get a pile of sunspots and a pile of sunspots
So the first and second piles of sunspots account for 1 / 3 of the total,
The sunspots in the third pile account for 1 / 4 of all sunspots
Then the third pile of sunspots accounts for 1 / 3 of the first and second pile of sunspots
So the third pile accounts for 1 / 3 × 1 / 3 = 1 / 9 of the total
The total number of sunspots is 1 / 3 + 1 / 9 = 4 / 9
1-4 / 9 = 5 / 9

There is a pile of black and white pieces, in which the number of black pieces is twice that of white pieces. If four black pieces and three white pieces are taken out of the pile at the same time,
So how many times after taking out, there are more than one white spot and 18 black spots?

3 × 2 = 6 pieces
6-4 = 2
(18-1 × 2) = 16
16 △ 2 = 8 times
Answer: eight times

There is a pile of black and white chessmen. The number of black chessmen is twice that of white chessmen. Four black chessmen and three white chessmen are taken out of the pile each time. After several times, the white chessmen are taken out, and there are 32 black chessmen left. How many chessmen are there in this pile?

Let's take x times. & nbsp; & nbsp; & nbsp; 3x × 2 = 4x + 32, & nbsp; & nbsp; & nbsp; 6x-4x = 32 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 16, (16 × 3) × (1 + 2) = 48 × 3, = 144 (pieces). A: there are 144 pieces in this pile

There are 50 red and white balls in total. They are arranged in the order of three red balls and two white balls. What are the percentages of the two color balls in the total number? What is the color of the 45th ball?
Major determinant

3 red and 2 white, 5 balls in a cycle, 50 balls just line up 10 times, so the total number of each point of the two colors of the ball is less
Red: 2 / (2 + 3) = 2 / 5
White: 3 / (2 + 3) = 3 / 5
The 45th ball is just the end of the cycle, so the 45th ball is white

There are two kinds of red and white balls in the box, two thirds of which are red balls and 20 are white balls. After taking out 15 red balls, how many are red balls in the total

Because the red ball accounts for two-thirds, so the white ball accounts for one-third, then there are 20 divided by one-third, which is equal to 60 balls
There are 40 white balls in 60 times two-thirds, 15 white balls in 15 and 25 white balls in 25. Dividing by (20 + 25) is five ninths
adopt!

The red ball is three times as big as the white ball, and the white ball is a fraction of the red ball
Boys are 2 / 7 more than girls. There are 20 girls. How many boys and girls are there

One third

There are three red balls, two white balls and five basketball balls in the bag. What's the possibility of touching the red ball? What's the possibility of touching the basketball? What's the possibility of touching the black ball? What's the possibility of touching the white ball?

In all, it's 10 balls
The probability of a red ball is 3 out of 10. Basketball is 1 out of 2. A white ball is 1 out of 5
The probability is the total number / number. So, there are 10 balls and 3 red balls. The probability is 3 out of 10

A box of beads, the first time out of the total number of 15 and 4, the second time out of the remaining 14 and 3, the third time out of the remaining 13 and 2, the fourth time out of the remaining 12 and 1, then there is still one in the box. How many original beads in the box?