Math problems, who will help me, it s urgent!

Because every student is a red pen and an orchid pen.

Then you can calculate 5 red pens in a pack, the unit price of each is 143 red pens in a pack, and the unit price of each pen is, and the blue pen is.

Then now it's time to combine.

47 students, 10 packs of 5 sticks are needed and 16 packs of 3 sticks are needed.

12 packs of red pens**10 61 610 Orchid pens 12 70 84016 packets of red pens**16 40 640, 16 47 752 Of course, it is impossible to say that all of them are bought with the same blue pens and the same red pens, if they are matched, it will be better. Here the red pen can be bought all, because in terms of the total ** and the unit price, it is the lowest ** to buy a pack of three. But if you buy 10 packs, there are 3 left, so you need to buy it together, that is, 9 packs of 5, plus 1 pack of 3, a total of 48, a total of 61 9 + 40 = 589

Let's talk about the blue pen. In terms of unit price, a pack of 5 is lower, but the total price of 16 packs is lower. Then you can use it with it.

That's 9 packs of 5 sticks, plus 1 pack of 3 sticks, then it's 48 sticks. Total price 9 70 47 677

To sum up, it takes at least 589 677 1266 to spend at least 589 677 1266, which is actually very simple, but in order to explain my algorithm to you clearly, so, I will write a lot, how about it, is the answer correct?

5 red pens in a pack of 61, then each is 61 5=

A pack of 5 blue pens is 70 yuan, then each is 70 5 = 143 red pens in a pack 40 3 =

3 blue pens in a pack 47 3=

Therefore, it is more cost-effective to buy a pack of 5 sticks under the conditions possible, and you need to buy 10 packs of red and blue packs that are all 5 packs, and you need money:

But there is more of this situation left.

So you can buy 9 packs of 5 red and blue packs, and then buy a 3-pack each.

So at least 1266 yuan.

Assuming that a pack of 5 sticks is used, it will cost 10 packs, and it will cost 61 * 10 + 70 * 10 = 1310 yuan.

Assuming that a pack of 3 sticks is used, it will cost 16 packs, and it will cost 40 * 16 + 47 * 16 = 1392 yuan.

Both of the above are wasteful.

Suppose you buy a pack of 5 sticks and a pack of 3 sticks together without wasting it, then you get a formula:

5x+3y=47

There are three sets of answers: x=1, y=12;x=4，y=9；x=7, y=4, and then calculate which way to use the red pen or the blue pen is the most economical.

Finally, it was concluded that the first group of red pens was used for a total of 541 yuan.

The blue pen is also the first one, totaling 634 yuan.

Then the teacher will spend at least 541 + 634 = 1175 yuan.

This proof is wrong.

To prove that tanx x increases monotonically, we can find the minimum value of the given interval of [xsec 2(x) -tan(x)].

xsec^2(x) -tan(x)]‘= sec^2(x) +2xsec^2(x)tan(x) -sec^2(x) = 2xsec^2(x)tan(x) >0

When x = 0, [xsec 2(x) -tan(x)] = 0, so [xsec 2(x) -tan(x)] 0 on (0, proof complete.

Set should be added to the drug x grams.

From the problem x 100=1 250 to get x = kg.

Solution: Set in 100 kg of water should be added to the medicine x kg.

1：250=x：100

x = kilogram = 400 grams.

Answer: 400 grams of medicine should be added to 100 kg of water.

70 per cent of the plenary session was done

90%-70%-(72%-70%)=18% can only do B, and 80%-70%-=10% can only do D

72%-70%=2% can do BC

Will do CD occupancy.

Then 30% of those who can't do A, 10% who can't do B, 28% who can't do C, and 20% who can't do D, then all the people who can't do it should be the plenum.

100%-(30%+10%+28%+20%)=12%I think so, I don't know if it's right, thank you for adopting it if you verify it correctly.

The title should be at least two words.