There are a few math problems that I don t know how to do, please help explain them, thank you 20

1.A number is divided by 3 by 2, 4 by 3, 5 by 4 by 4, and 5 by 4, and the maximum number within 500 that meets this condition is (479).

Then it can be seen that this number plus one is a multiple of 3,4,5, and the least common multiple of 3,4,5 is 3*4*5=60, then the minimum number is 60-1 = 59

If you find the maximum in 500, then 500 60 = 50 6 = 8 and 1 3, 8*60=480, 480-1=479 is the result.

2.The store buys a batch of shoes, each pair of purchase price, the price of yuan, when sold to only 5 pairs, has made a profit of 44 yuan, this batch of shoes a total of ( ) pairs.

Profit per pair of shoes - =

If you have made a profit of $44, then you have sold a total of 44 = not an integer.

I think it would be good if the purchase price was yuan, and the selling price would be good.

Profit per pair of shoes - =

If you have made a profit of $44, then you have sold 44 = 44

There are 5 pairs left, so there are 44+5 = 49 pairs in total.

3.There is a railway bridge 1000 meters long, a train passes on the bridge, it is measured that the train takes 120 seconds from the beginning of the bridge to the complete bottom of the bridge, and the time for the whole train to be completely on the bridge is 80 seconds, what is the speed and length of this train?

First of all, we must understand one point, that is, how to call a complete pass, that is, the locomotive to the bridge to the end of the train to the end of the bridge, then the distance traveled by the train is the bridge length + train length.

The train is completely on the bridge, which is understood as: the train just enters the bridge to the locomotive to Qiaowei, and the distance the train travels is the bridge length - the train length.

Let's say the train is x meters long.

1000 + x) :120 = (1000 - x):80

1000 + x) :3 = (1000 - x) :2

3000 - 3x = 2000 + 2x

1000 = 5x

x = 200 meters.

Speed = (1000 + 200) 120 = 10 m sec.

4.How many minutes does it take for a kilometer-long train to pass through a kilometer-long tunnel at a speed of 60 kilometers per hour?

and the third question.

Hours = minutes.

5.A book has 360 pages, Xiao Ming read 1 3 in the first week, and read the remaining 40% in the second week, so how many pages should I start reading in the third week?

In the first week, I read 1 3, which is 360*1 3=120 pages, and there are 2 3 left, which is 360-120=240 pages.

In the second week, I read the remaining 40%, which is 240 * 40% = 96 pages, for a total of 120 + 96 = 216 pages.

Then the third week also looks from the 217th.

First, the least common multiple of 3, 4, and 5 is within 60,500, and the largest common multiple is 480, so there is only 20 left. Assuming that this number is x, then from the above formula, x+1 is divisible by 3, 4, 5, and the minimum is 60, so x=59, then the largest number in 500 is 479.

Second, each pair of shoes made a profit of 44 yuan (the title is wrong, it should be 45 yuan), so 60 pairs were sold, a total of 65 pairs.

Third, the time to completely pass the bridge is the length of the train running the bridge plus the length of one body, and the length of the whole train on the bridge is the length of the bridge and the length of one body. That is to say, 120-80 = 40 seconds can run two car lengths. 40 2 = 20 seconds a body.

The train length is 1000 (120-20)*20=200 meters. The train speed is (1000+200) 120=100 m/s.

Fourth, the length of the tunnel and the train is the total distance = kilometers, which takes minutes.

Fifth, I watched 360*1 3=120 in the first week. There are also 360-120 = 240 pages. 240*40%=。That third week starts on page 217.

If you are dizzy, you will be 1 second slower.

1 499: The first question suggests starting with the third condition, which must be 499,494,489,484.

2 Each pair of profit yuan, the remaining 5 double value yuan, set a total of x pairs, (x-5)*, get x = 81 pairs.

3 Let the velocity x length y, 1000 + y = 120x, 1000-y = 80x, get x = 10 meters per second, length y = 200 meters.

4 Completely pass the need (hours, converted to minutes.

5 In the first week, I read 120 pages, leaving 240 pages, and in the second week, I read 240 * 40% = 96 pages, that is, I read a total of 120 + 96 = 216 pages, and in the third week, I started from 217 pages.

It's all like this, it's really unreasonable not to add points.

These questions are not too difficult, and the equations are all OK. The above is very well solved.

The first question gives you another method, this number +1 is a multiple of 3,4,5, so just find the greatest common multiple of 3,4,5 within 500 to -1.

499 doesn't seem right, right? Divided by three to one?

The first time I looked at my watch, the minute hand was clearly on the right half.

Since the minute hand rotates 360 degrees, the hour hand only rotates 30 degrees, so the speed of the minute hand is 12 times that of the hour hand, and the angle between the minute hand and the 12 o'clock direction is x degrees, according to the equation of 180-x+x 12=110 degrees between the hour hand and the minute hand 110 degrees

The solution is x=840 11

Converted to minutes (360 degrees is 60 minutes) is 140 11 minutes.

When I got home, it was not until seven o'clock, that is, the minute hand was on the left half.

In the same way, let the minute hand turn over y degrees (clockwise from 12 o'clock, greater than 180 degrees) y-180-y 12=110

The solution is y=290*12 11

The conversion to minutes is 580 for 11 minutes.

So the time to go out is 580 11-140 11 = 40 minutes (I play so many by hand, please give the best).

The minute hand travels 6 degrees per minute, and the hour hand travels every minute, and the difference in speed between the two is equivalent to a catch-up problem, in fact, the minute hand has traveled 110 degrees + 110 degrees (110 + 110) minutes more than the hour hand.

Step bu high up

The sides of the square are equal and are axisymmetric. If the length of an edge changes, its opposite edge changes accordingly. The two adjacent sides have their 1 2 and 1 4 respectively, that is, their opposite sides have increased their 1 2 and 1 4 accordingly.

So, the whole square becomes like this: two of the four sides have the original 1 2 added to each side, and each of the two sides has the original 1 4. Therefore, the circumference has increased by a total of (1 2) * 2 + (1 4) * 2 = 3 2 times.

Assuming that the side length of the original square is 1, the circumference of the new rectangle is 2*(, which is an increase from the original square (

One side increases the length of its original side by half, and the other side increases by half of the original side length, and the new shape is a rectangle. You can set the original side length to 1, then the side length of the increase is 3 2, and the half of the increase is 5 4, so that you can calculate, the original side length is 1, the perimeter is 4, and the length of both sides of the new figure is 3 2 and 5 4, then the perimeter is 3 + 5 2 =. The new perimeter is the original square circumference 4=, increased.

Note: The square in the title is adjacent to both sides, for example, the four sides of a square are in order, then 1 and 2 are adjacent, 2 is adjacent to 3, 3 is adjacent to 4, 4 is adjacent to 1, according to the title, we start from 1, 2 sides, 1 2 side is added to 1 2, 2 sides and 4 sides are adjacent to 1 side, so 1 and 4 sides are 5 4. Then the 3rd side is adjacent to the 2nd and 4th sides, so the 3rd side is 3 2, because the adjacent sides are 1 2 and 1 4 respectively.

All of the above calculations assume that the length of the original square side length is 1 meter.

Let's say the square side length is x (convenient point!) ）

A square is a special shape of a rectangle (i.e., a rectangle), and when one side is grown, the opposite side of the rectangle will grow accordingly!

So when the two sides grow and sum respectively, the corresponding opposite side will also grow and so grow.

It turned out to be a square, with equal adjacent sides. Set to a.

An edge is increased by 1 2 for 3 2a, and an edge is increased by 1 4 for 5 4a.

The circumference of the new rectangle = a * (3 2 + 5 4) * 2 = 22 4a

The original circumference was 4a.

increased by 22 4a-4a=5 4a; (5 4a) 4a = 5 16 increased by 5 16

＝21*101，202＝101*2；212121=10101*21，,50505=10101*5.。。and = 1 21 + 2 21 + 5 21 + 13 21 = 1,30

3. Set the price of basketball x, the price of football y, and the remaining money to buy a football, then there is 8x=12y=6x+ay, and ay=2x, 6x=3ay, 12y=4ay, then a is 3

14 = 2 7<3 10, so the concentration after adding is smaller than 30%.

5. Set up forests to complete x every day, and strong to complete y every day. Then 3(x+y)=1,2x+y=1 2 solves the equation system to obtain x=1 6,y=1 6, and it takes 6 days to complete it alone.

6. Set the speed of the passenger car to be x kilometers per hour, and the two places of A and B are Y kilometers.

6x=7 8y,6(x-15)=1 2+54 to get y=384 km.

7. Calculate the four situations yourself.

robby006 is exactly right! Top it.

1.There are a total of x square earth. (x=

2.The interval of the workshop is m, the speed of the vehicle is x, and the speed of the person is y

m (x+y) = 10 m (x-y) = 15 to get x y = 5 1

Therefore, the car takes 24 minutes, and the person needs 24 * 5 = 120 minutes to walk the whole way. So the two met 60 minutes later.

3.In the extreme case, the time is equal. Set the walking speed to x, the cycling speed to 4x, and the distance from the mall to the park y

3/x+(3+y)/4x = y/x

y=5, so the mall to the park is at least 5km

I've learned the equations.

1. If the total earthwork is x, then team A digs x 36 square meters of soil every day, and team B digs x 45 square meters of soil every day;

The two teams work at the same time, digging x 36 + x 45 = x 20 square soil every day;

If the work efficiency is increased by 20%, the two teams dig x 20 * (1 + 20%) = 3 x 50 square meters of soil every day;

After completing 3 5, there is 2 5 left, but it took 12 days to complete, which means that (2 5*x) 12=x 30 square soil was dug every day in these 12 days;

And because the difference with the rain before and after the rain is 50 square soil, then.

3x 50-x 30=50 solution to x=1875 square soil.

2. Let two people meet in x minutes. And because the two people have the same speed, it takes one person 2x minutes to complete the journey;

Assuming that the whole journey is 1, the speed of the person is 1 2x, and the speed of the car is 1 24;

Suppose two people and two cars start driving in opposite directions at 0:00 at the same time, and after 10 minutes, they each leave.

1 2x)*10=5 x, at which point two trams meet them at the same time;

After another 5 minutes, Xiao Ming walked away again (1 2x)*5=5 2x, and then the car that met Xiao Hua caught up with Xiao Ming;

So, the distance traveled by the car in 5 minutes is 5 x + 5 x + 5 2x = 25 2x;

And because the speed of the car is 1 24, 5 minutes the car travels 5 24;

So 25 2x = 5 24, the solution is x = 60 minutes.

3. The distance from the mall to the park is y, and the walking speed of two people is x, and the riding speed of two people is 4x;

In the first scenario, the total time is 3 x+(y+3) 4x;

In the second scenario, the total time is y x;

So according to the title, then y x 3 x+(y+3) 4x;

If 1 x is eliminated on both sides at the same time, then y 3+(y+3) 4

The solution is y 5, so at least 5 km.

If you understand it, remove the text and it's the equation.

Let Xiao Li's speed of rushing back be x

3(x-6)=6*2

x = 10 km-h.

Set the length of the team s

s/(10-6)+s/(10+6)=

Find s = km = 400 meters.

Let's say B produced x blade holders during this time, then B produced 50x blades.

Then B's profit is 50x multiplied plus x multiplied by (1-5), and A's profit is 8400 times it.

The profit between the two is 2 times the relationship.

So 8400 multiplied by 2 equals 50x multiplied plus x multiplied by (1-5).

i.e. 8400 (.)

Solve the equation to get:

The solution is x=400 and y=20000

A: Factory B sold 400 knife holders and 20,000 blades.