Ask a morning math problem for the summer vacation park in the fifth grade of elementary school.

There are 381 red lights in total, and he also said that the number of red lights has multiplied, that is, if there are x red lights on the first floor, there will be 2x on the second floor. 3 layers is 2 2 x , which is 4 x ,......Let them add up 1+2+4+8+16+32+64=127x

381 127 = 3 (pcs), that is.

There are 3 (pieces) on the first floor

There are 3 2 = 6 (pieces) in 2 layers

There are 6 2 = 12 (pcs) on the 3rd floor

There are 12 2 = 24 (pcs) on the 4th floor

There are 24 2 = 48 (pcs) on the 5th floor

There are 48 2 = 96 (pcs) on the 6th floor

There are 96 2 = 192 (pcs) on the 7th floor

Inspection: 3 + 6 + 12 + 24 + 48 + 96 + 192 = 381 Answer: There are 24 red lights on the 4th floor.

The seventh floor of the Fire Tree Silver Flower Building shows that there are 7 numbers in this number series;

The layers of red lights are multiplied, indicating that the number series is equal to multiplication, that is, 2 times increment;

There are a total of 381 red lights, indicating that the sum of this series is 381;

If you ask how many red lights are on the fourth floor, what is the fourth number?

Solution: Let the first layer be x red lights.

127x=381

x=3 (pcs).

The fourth layer is 2 2 2 x = 8 3 = 24 (pcs).

A: There are 24 red lights on the fourth floor.

If there are x red lights on the first layer, then the second layer has 2x, the third layer has 4x, the fourth layer has 8x, the fifth layer has 16x, the sixth layer has 32x, and the seventh layer has 64x, since x+2x+4x+8x+16x+32x+64x=381

Get x=3, so the fourth layer has 8x=24

24 pcs. If there are x on the first floor, there will be seven floors in order.

x，2x，4x，8x，16x，32x，64x。

Adding 127x equals 381

Then x is equal to 3, and there are 24 in the fourth layer.

2、 -2ab

6、 -4ab/5c

7. For the apex angles, equal.

9. (a+1)(1-a)(a+1).

10、 2/a(a+2)

Option 1 – 5 cabcc

6——8 cab

Calculation (the answer is in order).

2x(a-b)

a+9b)(9a+b)

x(x-1) square.

xz(x-2y) square.

m-n).

y+3 2) square.

2 (x+1 2) square.

x+y-7).

m+2n) square (m-2n).

x+2) square (x-2) square.

x＜3 x≥15/4

x≤-4 2＜x＜15

Draw slightly a -7

108 and 52

5a-7＜0 x＞2

x-1 y/x+y

ab/a+b

Option 1 – 8 DCCCCADC

Calculate -b square a

Remember to give me extra points.

Classmates, if you want to copy the answer, there is no need, if you don't understand the question to put the question up, there are many masters here, I believe they will help you solve it.

set, my sister walked for x minutes.

Then: Pressing the pants to pay homage to the title is equivalent to her sparrows walking two full journeys (i.e., one round trip).

50*x+150*x=800*2

x = 8 minutes.

A: My sister walked for 8 minutes.

Arithmetic solution: The two walked a total of 800*2=1600 meters.

It took 1600 (150+50) = 8 minutes. Sisters are the same as Hu Sui.

1 gift box needs (10+15)*2+8*4+25=107 cm.

10 meters = 10 * 100 = 1000 cm.

1000 107 = 9 surplus 37

This rope can tie up to 9 gift boxes.

I calculated that it should be nine.

I think it takes rice to bundle a gift box, so I can bundle 9 gift boxes separately. If you bundle together, you can bundle up to 29 gift boxes.

Because 3 is their least common factor, Huai Shi does not.

1008 divided by 3 = 336

1260 divided by 3 = 420

1368 divided by 3 = 462

1134 divided by 3 = 378

They are exactly divisible by 3, so 3 is the common factor for the nucleus to do them, and the answer comes out!

Hope it helps!

Divide by 3 to take the first place, and the password is 3, 4, 4