All the concepts and formulas of elementary school mathematics. Thank you!

You can go to the library and look for the ones I found before.

As mentioned above, divide the number (18-15) by the original 18 seconds of the unit, carefully calculate and keep four decimal places.

Solution: 27 km = 2,700,000 cm.

The distance on the map is x centimeters.

1:600000=x：2700000

x=2700000x1÷600000

x = A: The distance on the graph is in centimeters.

Solution: Suppose the train can travel x kilometers per hour.

1+25%)x=150

x=120A: The train can travel 120 kilometers per hour.

To process a batch of parts, it takes 8 days for the master to do it alone, and 1 8 apprentices to do it alone in 10 days, 1 10 a day

Now it is done by the master and the apprentice together, 1 8+1 10 = ( 5+4) 40 = 9 40 in a day

Halfway through, the master took a leave of absence for 1 day due to a meeting, and set up a day for the apprentices to finish this batch of parts.

Then the master did a-1 day and did (a-1) 8, and the apprentice did a 10

a/10 + a-1)/8 = 1

8a + 10a -10 = 80

18a = 90

a = 5 days.

Set the apprentice to do x days, then the master to do x - 1 day, then.

x-1）/8+x/10=1

x/8+x/10=1+1/8

9x/40=9/8

x=9/8×40/9

x = 5 apprentices do 5 days.

Here's how to solve it:

The master's work efficiency is 1 8, and the apprentice's work efficiency is 1 10 The equation is:

It took the apprentice 5 days to complete.

If the total project is "1", then the master will do 1 8 a day, and the apprentice will do 1 10 a day, 1-1 10) (1 8 + 1 10) = (9 10) (9 40) = 4 (days).

4+1=5 (days).

The master's work efficiency is 1 8, and the apprentice's work efficiency is 1 10 The equation is:

5 and 5/36

It took the apprentice 5 and 5/36 days to complete.

I want to say that the above people have not seen the question clearly, it is the master who went out for a day, so the remaining workload is (1-1 8).

So the amount of work that the master and the apprentice do together is 7 8, and the time is (1-1 8) (1 8+1 10).

The remaining workload is 1 8, and the time required for the apprentice to complete it alone: (1 8) (1 10) So the total time taken by the apprentice is: (1-1 8) (1 8 + 1 10) + (1 8) (1 10) = 185 36

The master's work efficiency is 1 8, and the apprentice's work efficiency is 1 10 (1-1 10) (1 8+1 10).

It took the apprentice 5 days to complete.

The master's work efficiency is 1 8, the apprentice is 1 10, and the apprentice does it for 5 days.