There are 90 tons of grain in warehouse A and 60 tons in warehouse B. how many tons are taken out of warehouse A to warehouse B so that the weight of grain in warehouse A is two fifths of that in warehouse B

There are 90 tons of grain in warehouse A and 60 tons in warehouse B. how many tons are taken out of warehouse A to warehouse B so that the weight of grain in warehouse A is two fifths of that in warehouse B

（90-x）/（60+x）=2/5
X = 330 / 7 = 49.1 tons
90-x = 2/5(60+x)
Why multiply 2 / 5 by 60 and add the sum of X?
There are 13 people in an extracurricular activity group, including 8 boys and 5 girls, and each of them has a team leader. Now, five people are selected from the group to host an activity. How many choices are there according to the following conditions\
1. Only one girl?
2. Two captains elected?
3. At least one captain is elected?
4. At least two girls were elected?
5. Not only the team leader, but also the female students?
There are 5 choices for boys and 8 choices for girls
2. Two team leaders choose two from two, one method, the remaining 11 candidates are three, C (11,3) = 165, so there are 165
3. There are 1287 kinds of C (13,5) = 1287, among which C (11,5) = 462, so there are 1287-462 = 825
4. There are 1287 kinds of C (13,5) = unconditional choice, among which there are no girls (that is, boys choose 5 out of 8) with C (8,5) = 56
There is a girl (4 men and 1 woman) who has C (8,4) * C (5,1) = 350, so there are 1287-56-350 = 881 species
5. There are totally C (13,5) = 1287 kinds of unconditional selection, among which there is no team leader, C (11,5) = 462, no girl = 56, and there is no team leader and no girl, C (7,5) = 21 kinds, which are repeated twice, so the answer is 1287-56-462 + 21 = 790
The ratio of number a to number B is 3 to 5. The number a accounts for a few parts of number a and number B, and the number B accounts for a few parts of the sum of number a and number B
Number a accounts for 2 / 5 of number B, and number B accounts for 5 / 7 of the sum of number a and number B
3 out of 8 5 out of 8
1、 There are 126 people in the second workshop and 92 people in the first and the second workshops. How many people are there in each workshop?
Analysis: it is known that there are 126 people in the first and second workshops, and there are 92 people in two thirds of the number in the first workshop and five sixths of the number in the second workshop
Let one be x and two be y
x+y=126
2/3x+5/6=92
The joint solution can be used to find X and y
Two thirds of a number plus 75% of it equals 34. What's the number
Let this number be x, then 2x / 3 + 75% x = 34
75%=75/100=3/4
So (2 / 3 + 3 / 4) x = 34
That is 17x / 12 = 34 (general)
The solution is x = 34 × 12 / 17 = 24
34÷(2／3＋75％)=24
Let this number be x, so there is 2x / 3 + 75% x = 34, and the solution is x = 24
There are 85 people in the chorus team of art experimental school, 8 less than 3 times of the dance team. How many people are there in the dance team? (list 3 relations and 3 equations.)
If the number of dancers is x
1、 85=3*X-8
2、 85+8=3*X
3、 X=（85+8）/3
75% of a number is equal to 1 / 3 of 120
120x1 / 3 △ 75% = 53 and 1 / 3
75X = 120 / 3 = 40, so x = 160 / 3
one hundred and sixty-thirds
120 × 1 / 3 △ 75% = 53 and 1 / 3
40/75