Solving the math problem, I figured it out, but it was different from the answer 10

c: after the first time: even numbers are extinguished, odd numbers are bright; After the second time:

It is both an even number and a triple brightness, i.e., a multiple of six brightness; odd and not a multiple of three bright; So the ordinal numbers of Liang are 6n and 6n+, -1; i.e. half; After the third time: the multiple of half of five is on, and the multiple of half of five is off, (because the ordinal number of the second time is regularly arranged, and half of the multiple of five is also on), so there is no change in the number of lights. 1997 = 6 * 333 - 1 so the last light is on, (1997-1) 2 = 998, a total of 998 + 1 = 999 lights on.

The answer is wrong, (1997-1) 2=998 1997-998=999 (1997-2) 3=665 999-665=334 (1997-2) 5=399 334-399=-65 1997 (2*3)=332 (rounded) 1997 (2*5)=199 (rounded) 1997 (3*5)=133 (rounded) 1997 (2*3*5)=66 (rounded).

Why should multiples of 30 be multiplied by 2? I'm going to explain, because we added multiples of 15 and 6, and 15 and 6 are both factors of 30, so we added two multiples of 30. The landlord chooses me!

I'm also counting 533. Don't forget to notify you when you know the correct result. Then count.

The first one, of course, is wrong, there is only one variable x, and the sum of is 0 and not the product is 0

The second way is right, and the answer is that there is no solution. The first calculation algorithm is fine, the sum of the two non-negative numbers is zero, and the two non-negative numbers are zero, but the previous code is both zero at the same time, not either a is zero or b is the modulo row which zero. To take the intersection of two non-negative numbers that are both zero, =5 and =-3 2 have no intersection, so there is no solution.

The second is to give way to the radical pair. Finding the limit is only the addition and subtraction of the ability to divide the slide, and there is no other calculation and calculation.

For another example, x tends to 0, and socks seek (sinx) the limit of x. As you think.

sinx=0,0 x=0, so it tends to 0

x=0, sinx 0, so it tends to infinity.

Actually, neither is true, x tends to 0, and (sinx) the limit of x is 1

The second approach is correct.

Think of the exponent of 3 as x, and then transform the bracketed n into one of the 2x points, and multiply the two.

In the other method, although n tends to be infinite, it is necessary to take into account the n outside the parentheses, and if the direct core finch is equal to, then the calculation result will be incorrect.

Solution: A is issued in the first place.

125 (m).

A and B.

40 (m) B ground A section hair.

60 (m) B ground B paragraph B.

90 (m).

20 small tables, 30 small stools, small tables are 8 yuan more expensive than small stools, and 2860 yuan are shared.

Solution: Because the small table is 8 yuan more expensive than the small stool, so assuming that the ** of the small stool is x yuan, then the ** of the small table is (x+8) yuan, so .

30x+(x+8)×20＝2860

30x+20x＝2860-20×8

30+20)x＝2860-20×8

x (2860-20 8) (30+20) solution: x 34

That is, the small stool ** is 34 yuan, and the small table ** is 34 + 8 42 yuan.

Solution: Each small table is 8 yuan more expensive than a small stool, and 20 small tables are 8x20 = 160 yuan, 1860-160 = 1700 yuan. This 1700 yuan is the sum of the small stool and the small table under the same ** 1700 (20 ten 30) = 34 yuan, and the small table ** two 34 ten eight two 42 yuan.

At least yes, how can there be two answers.

If you pay 175 yuan to buy a piece of clothing, it may be 10 yuan for 100 provinces, then the original price is 175 + 10 = 185 yuan, or it may be 30 yuan for 200 provinces, then the original price is 175 + 30 = 205 yuan.

200 provinces 30, equivalent to 15 per 100 provinces, 300 provinces 50, equivalent to 50 per 100 provinces 3>15, buy things as much as possible according to the maximum satisfaction value.

1) When the original price is 185 yuan:

185 3 = 555, press 300 once, 200 once, save 50 + 30 = 80 yuan, 555-80 = 475 yuan.

2) When the original price is 205 yuan, 205 3 = 615, calculated twice according to 300, saving 50 + 50 = 100 yuan, 605-100 = 505 yuan" 475 yuan.

It costs at least 475 yuan to buy 3 shirts. Note that it is the least needed, not the need, so choose the least item.

185 3 = 555 yuan.

The 555 can meet the following forms.

If you meet 100, you can save 5 10 = 50 yuan, and pay 555-50 = 505 yuan If you meet 100 and 200 at 1 time, you can save 3 10 + 30 = 60 yuan, and you can pay 555-60 = 495 yuan.

If you meet 100 times and 300 at one time, you can save 2 10 + 50 = 70 yuan, and pay 555-70 = 485 yuan.

If you meet 200 times and 300 at a time, you can save 30 + 50 = 80 yuan, and pay 555-80 = 475 yuan.

To sum up, of course, it is the 4th province to choose.

The answer is B

Choose A3 shirts, a total of 525 yuan, divided into 300 and 225 parts, 300-50 = 250

This question is a bit imprecise, there are two possibilities for paying 175 yuan before, one is 205 yuan for that dress, and the other is 185 yuan, and the two will get different answers. So you're right.

The first algorithm is correct, and the total mass of iron is calculated and compared to the mass of the total oxide, and the result is definitely the correct mass fraction.

The second algorithm is wrong, because in the parentheses, you are dividing the width and covering to find the two kinds of mass fractions, and then adding, can you add two different mass fractions? Here you have made a mistake, not to mention dividing it by 29.

If you think about it, think about it along this line of thought, and you will find the second type of mistake.

I hope mine can help you.