A comprehensive elementary school math problem A primary school math problem

Math problems in the renminbi.

One day, I went to the mall with my mother. Mom went into the supermarket to buy something and asked me to stand at the place where I paid and wait for her. I didn't have anything to do, just watched the salesman and aunt collect the money.

Looking at it, I suddenly found that the money collected by the salesman aunt was 1 yuan, 2 yuan, 5 yuan, 10 yuan, 20 yuan, and 50 yuan, and I felt very strange: why is there no 3 yuan, 4 yuan, 6 yuan, 7 yuan, 8 yuan, 9 yuan or 30 yuan, 40 yuan, 60 yuan? I quickly ran to ask my mother, and my mother encouraged me to say

Use your brain and think about it, Mom believes you can figure out why for yourself. I settled down and thought about it carefully. After a while, I jumped for joy :

I know, because as long as there are 1 yuan, 2 yuan, and 5 yuan, you can form 3 yuan, 4 yuan, 6 yuan, 7 yuan, 8 yuan, and 9 yuan at will, and as long as you have 10 yuan, 20 yuan, and 50 yuan, you can also form 30 yuan, 40 yuan, and 60 yuan, and ......My mother nodded and asked me another question: "If it's just to be able to combine at will, isn't it enough for only 1 yuan?" Why do you need 2 yuan or 5 yuan?

I said, "It's not convenient to use just 1 yuan to form a larger number." My mother smiled with satisfaction, and praised me for being observant and using my brain, and I was more comfortable listening to it than eating my favorite ice cream.

Here, I would also like to tell other children: in fact, there are math problems everywhere in life, as long as you.

If not, tell me what grade you have, I'm helping you!

Take a look at the "Cool Shadow Mode" you know.

Let the tens be x and the single digits be 2x. Then the original two-digit number is 10x+2x, and the converted two-digit number is 20x+x:

The equation is: 20x+x-(10x+2x)=36 solution equation: x=4

Then the original number is 10x+2x=48

Solution: If the number in the tenth place is x, then the number in the single place is 2x

10×2x+x-（10x+2x）=36

20x+x-12x=36

9x=36x=44 2=8 The number of tens is 4 and the number of single digits is 8, then the number is 48

Let the tens be m and the single digits be n, then:

n=2m10n+m）-（10m-n）=36

Solution: m=4, n=8So, the original number is 48

If the ten digits are x, then the digit in the single digit is 2x

2x*10+x-（x*10+2x）=36

21x-12x=36

x=44*2=8

The original digital 48

Solution: If the ten digits are x, then the digits are 2x

2x×10＋x－（10x＋2x）＝36

9x＝36x＝4………Ten digits.

2x＝2×8＝8………Single digits.

So, the two-digit number sought is 48

If ten is x, then you are 2x

10*2x+x-36=10x+2x

21x-36=12x

21x-12x=36

9x=36x=4, this number is 48

Hello qwezsea :

Solution: Let the ten digits be x and the single digit be 2x

2x×10＋x）－（10x＋2x）＝3621x－12x＝36

9x 36x 4 digits are: 2 4 8

This two-digit number is:

Let the height of the large cylinder be h, the radius of the bottom surface be r, and its surface area s1'=2 r 2+2 r*h=2 (r 2+rh), then the surface area of the cuboid is: s1=4*2r*h+2*2r*2r=8(r 2+rh), let the height of the small cylinder be h, the bottom radius is r, and its surface area is s2'=2 r 2+2 r*h=2 (r 2+rh), then the surface area of the cuboid is: s2=4*2r*h+2*2r*2r=8(r 2+rh), s1-s2=8(r 2+rh)-8(r 2-rh)=,—》r 2+rh)-(r 2-rh)=,—》s1'-s2'=2π(r^2+rh)-2π(r^2+rh)=2π*。

Box surface area = 2a2 + 4ab

Cylindrical surface area = 2 (a 2) 2 + ab = 4 (2a 2 + 4 ab).

So the cylindrical surface area difference = * 4 =

Let the left bottom side length be a1, the edge length be b1, the right bottom edge length is a2, and the edge length is b2, so the difference between the surface area of the two cuboids = (a1 +2a1b1-a2 -2a2b2)*2=

Extracting the common factor 2 gives d= 2*(a1 -a2 +2a1b1-2a2b2)= 2*

If you don't understand it, you can ask.

Hello. The price of the book is yuan.

Brother 0 yuan.

Younger brother Yuan. The younger brother is only missing 1 point, and the two of them together are not enough money, which means that the elder brother doesn't even have 1 penny, so the elder brother has no money at all, so it can be seen that the price of the book is exactly 5 yuan, and the younger brother's money is 4 yuan, 9 jiao and 9 cents.

The younger brother is only missing 1 point, but the money added up by the two is not enough to buy a book, so it can be seen that the elder brother doesn't even have 1 penny, so the elder brother has no money at all, so the price of the book is exactly 5 yuan.

The combined money of the two is not enough to buy a book, so it can be seen that the elder brother doesn't even have 1 penny, so the elder brother has no money at all, so the price of the book is exactly 5 yuan.