A: The master can complete X pieces in one day, and the apprentice can complete Y pieces in one day. The total number of parts is S.
s =(x+y)* 15 = = & gt； y=s/ 15-x
s- 10y= 17x
s- 10 *(s/ 15-x)= 17x
s-2s/3+ 10x= 17x
s/3=7x
s=2 1x
Therefore, it takes 2 1 day for the apprentice to complete this batch of parts alone.
2. The senior students took 40% of the original story books in the school, and the administrator bought 180 books from the bookstore, just taking 25% of the books. How many books did the senior students take?
Answer: suppose there are x story books.
25%*(40%*x)= 180
1/4*2x/5= 180
2x/20= 180
x= 1800
The number of books brought by senior students is 1800*40%=720.
So, the seniors took 720 copies.
3. The store bought some soccer balls and sold them at 1 12% of the original price, with a unit price of 67.2 yuan each. When 50 footballs were sold, the full cost was recovered. How many footballs did the shop buy?
A: suppose there are x footballs, and the original unit price is S.
1 12%*s=67.2 s=60
60x=50*67.2
x=56
So, the store bought 56 footballs.
4, two engineering teams, one team has 120 people, 20% of the number of the first team is transferred to the second team, and two-thirds of the number of the second team is exactly three-quarters of the number of the first team. How many people are there in the second team?
A: let the original number of the second team be X.
(x+ 120 * 20%)* 2/3 =( 120- 120 * 20%)* 3/4
x=84
The number of people less than the first team is 120-84=36.
5. Group A and Group B work together on a project, and can complete 9/40 of the tasks every time. Team a worked alone for 3 days, team b worked alone for 5 days, and the remaining one-eighth of the tasks were not completed. If all the projects are completed by team B alone, how many days will it take?
A:
[1-1/8-3× (9/40)] ⊙ (5-3) =110 for team b to complete all projects every day.
Team B does it alone, and it takes1÷ (110) =10 days to complete it.