Solve a math problem, it s better to talk about it again, thank you!

Regardless of how many parts there are, think simply: the master does all the 1 8 per hour, and the apprentice does all the 1 12 per hour, so if two people do it together, 1 hour can do a total of 1 8 + 1 12 = 5 24, then the time required for the master and apprentice to do it together is 1 divided by 5 24 = hours.

The apprentice did 240 per hour, so the apprentice did 240 per hour.

From the question, it can be seen that the apprentice's work efficiency is 1 12, and the master's work efficiency is 1 8, so it takes 1 divided by 1 12 + 1 8 = 24 5 days to complete, and the apprentice will process 240 divided by 24 5 = 50 parts per hour. Kneel and beg.

Because it is a mobile phone, it is a bit troublesome to do it together Master and apprentice, a total of 1 (1 12 + 1 8) = time, the apprentice made 240 parts during this time, so 240 parts per hour.

Calculate the time to complete the task first, the master can complete the total number of 1 8 per hour, the apprentice is 1 12, and the master and apprentice can complete the total number of 1 8 + 1 12 = 5 24 per hour, which means that the time to complete the task is 24 5 hours.

The apprentice completed 240 in 24-5 hours.

The apprentice processes 240 (24 5) = 50 per hour.

If the apprentice processes x parts per hour, the master processes (12x 8) parts per hour.

Column equation: (12x 8) (240 x) + 240 = 12x

Solution: x=50

Set the square area with n tiles on the edge, then.

From the meaning of the title. n+1)^2-n^2=180+21

n^2+2n+1-n^2=201

2n=200

n=100 (block).

n^2+180

10180 (block).

So there are a total of 10,180 tiles in this batch.

2.Because take a random array of 3 cards on which the sum of the numbers is equal to 10:

1,3,6),1, 4, 5),2, 3, 5) are 3 groups, so randomly take the probability that the sum of the numbers on 3 cards is equal to 10.

(1) The side length is x blocks, and the batch of tiles has a total of y blocks.

x^2 +180 = y;

x+1)^2 -21 = y;

x = 100

y = (c) 10180 blocks.

2) Permutations and combinations.

3 of the 6 cards are randomly selected, a total of 6 * 5 * 4 3 * 2 = 20 ways to draw.

Composition 10 has 4 results.

Grow 1 times per day.

Then his growth formula is 2 cm for 12 days, 4 cm for 13 days, 8 cm for 14 days, and 16 cm for 15 days. It takes 16 days.

The math is calculated from 12 days of the earth.

2 to the nth power is 16

n = 4 so also 15 days.

Let pb x

The square side length is 2

Then the P point is PE BC (E is the point on the CD edge).

de＝2-x pd＝2＋x

PE de DP in DPE

i.e. 2 (2 x) 2 x).

Solution x so sin pde 4 5

And sin adm 1 5

cos∠adm＝2/√5

sin∠pde＝2sin∠adm×cos∠adm＝sin2∠adm∴∠pdc＝2∠adm

This is a question of several grades.,I can't understand Sa.。。

Two scenarios:

First, let the middle number be x and be even.

Then the three numbers are x-2 -x x+2 and the three numbers are added to give x=-201, then the three numbers are -203, 201, -199

Second, let the middle number be x and be odd.

Then the three numbers are x-2 -x x+2 and the three numbers are added to give x=-201, then the three numbers are -203, 201, -199

The result is the same.

The rule is: [(1) (n+1)] 2n+1), and the sum of the two numbers before and after each number is equal to -2 times the middle number.

The sum of the three adjacent numbers is -201, then the middle number is -201 (-2+1)=201

The former number is -199 and the latter number is -203

So these three numbers are -199, 201, -203

Observe the trend of this series, the difference series, and find its general formula, an=(-1)n (2n-1).

So let the number in the middle of the three numbers be x, then 3x=-201, and the solution is x=-67, so these three numbers are 65, -67, 69

The first of these three adjacent numbers is x, then the second is -(x+2), and the third is x+4x-(x+2)+x+4=-201

x+2=-201

x=-203

These three numbers are -199 201 -203

The second root and the first root are a total of rice.

d, you can set Xiao Ming's date of birth as x, then Xiao Li's date of birth is x+7 or x+14 or x+21 (both are Fridays, so the difference is a multiple of 7, you should be able to understand).

Then, one by one, x is an integer, and only x+(x+14)=22, that is, x=4

Then Xiaoli's date of birth is x+14=4+14=18

On Sunday, there is no answer!

If the date of the first Friday is x, then the next Friday will be x+7, x+14, x+21, x+28

All add up to 80, i.e. x+x+7+x+14+x+21+x+28=80, which gives x=2

Then the last Friday is x+28=30, and May has 31 days, then the 31st is Saturday, and June 1st is Sunday.

Xiao Ming is No. 4, Xiao Li is No. 18, so choose D

Children's Day is a Sunday.

1, Xiaoli's A

2. June 1st of that year should be Sunday.