How to solve this 5th grade math problem? 10

Connected to AF, the drain time can be equivalent to the area of a triangle (the larger the area, the longer the drain time and the time is proportional to the area of the pool).

ef:fc=2:3 bf:fd=7:3

Let the drainage time of AFD be T1, and the drainage time of AFE is T2T2:9+T1=EF:FC=2:3

t1:14+t2=fd:bf=3:7

Solve binary linear equations.

t1=12，t2=14

It takes 12 + 14 = 26 hours, find.

Solution: Set the well to a depth of x meters.

x+2)*4=(x-2)*5

The solution is x=18

then (x+2)*4=80

A: The length of the rope is 80 meters, and the depth of the well is 18 meters.

Xiaojun buys things in yuan. The key is to figure out the unit price per pen and per cartridge. Because the money used is the same, the more you buy must be cheaper. So the ** of the pen case is more expensive. Yuan branch yuan.

Total amount of money: yuan).

Fountain pen unit price: yuan).

Unit price of pen box: yuan).

Because the unit price of the pen case is greater than the unit price of the fountain pen.

So the pen case is more expensive.

The unit price of the fountain pen (yuan.

The unit price of the pen case (the yuan pen case is expensive.

This is the total amount of money for the small army.

This is the money to buy a pen.

This is the money to buy a pencil case.

Therefore, it is more expensive to buy a pencil case.

Pencil cases are more expensive because: . . Think for yourself.

This is regular.

1) Through the first few numbers, it can be found that as long as the last number is added, it is equal to 1, so 1-1 512 = 511 512 can be used

It can also be split into (1-1 2) + (1 2-1 4) + (1 4-1 8) + ....1/256-1/512）

Then remove the brackets (preceded by the + unchanged sign), add and subtract to offset, and 1-1 512 = 511 512 can be obtained

2) It can be split into (3+4) 12-(4+5) 20-(5+6) 30-(6+7) 42

When the brackets are removed, it becomes (1 4 + 1 3) - (1 5 + 1 4) - (1 6 + 1 5) - (1 7 + 1 6).

Use the commutative law of addition to exchange the position of the addition in the parentheses, and then remove the parentheses (preceded by - to change the sign), and add and subtract to cancel.

It can be obtained that 1 3-1 7 = 4 21 (the two fractional units are added and subtracted, the product of the denominator is the denominator, and the sum of the denominator (difference) is the numerator).

2 1-4 1-8 1-16 1-32 1-64 1-128 1-256 1-512 1-1024 1 Yes.

Solution: Original = 1 2-1 4-1 8-1 16-......1 512-1 1024 2 Original = 1-1 2-1 4-1 8-1 16-......1 512 2 Original - Original = 1 + (-1 2 - 1 2) + (1 4 + 1 4) + (1 8 + 1 8) + ...1 512 + 1 512) +1 1024 =1-1+1 1024 =1 1024 And: 2 Primitive-Primitive=....

Verbose] find the value of 1-1 2-1 4-1 8-1 16-1 32-1 64-1 128-1 256-1 512.

Question 1:

Directly remove the brackets, and the middle one can be offset.

1, the original formula = 511 512, find the law, such as: 1 2 + 1 4 = 3 4, 1 2 + 1 4 + 1 8 = 7 8, we first observe the calculation results, the difference between the numerator and the denominator is 1, and then see that the numerator of these two equations is 1, and the denominator is a multiple of 2, so the denominator of the final fraction remains unchanged, and the numerator can be denominator-1.

2: Original = (3+4) 12-(4+5) 20+(5+6) 30-(6+7) 42

The first one should be 511 512You add a few more times and you add a pattern.

Is this really a math problem in elementary school?

Solution: The sum of five numbers.

38 3 = 114 – the sum of the first three numbers.

52 3 = 156 – the sum of the last three numbers.

It stands to reason that the sum of the five numbers should be the sum of the first two numbers plus the sum of the last three numbers (or vice versa), but if an extra middle number is counted in the question, the middle number is counted twice, and the sum of the first three numbers plus the sum of the last three numbers is greater than the sum of the five numbers, and the extra number is the number of multiple counts (that is, the number in between).

A: The middle number is 48.

The sum of the first three numbers and the sum of the last three numbers are repeated by the middle number once, and the subtraction of the middle number is equal to the sum of the total five numbers.

The sum of the first three numbers + the sum of the last three numbers - middle number = sum of total 38 3 + 52 3 - middle number =

114 + 156 - middle number = 222

Median number = 48

The sum of five numbers:

The sum of the first three numbers: 38*3=114

The sum of the last three numbers: 52*3=156

The sum of the first three numbers plus the sum of the last three numbers = the sum of the five numbers + the middle number, so the middle number = 114 + 156-222 = 48

The sum of the first three numbers: 38 3 = 114

The sum of the last three numbers: 52 3 = 156

In both sums are included medians.

Decimeter = 25 cm, decimeter = 36 cm, cuboid oil drum volume = 25 * 25 * 36 = 22500 cubic centimeters = 22500 ml, 22500 750 = 30 bottles.

A: It can be filled with 30 bottles.

1100 * (1 = 1 5) = 880,880 * (1-3 4) = 220,200 * (1-1 2) = 110 km.

There are still 110 kilometers left.

On the first day, 220 km were walked, 880 km remained, on the second day 660 km was left, 220 km remained, and on the third day, 110 km were left untraveled.

1. A rectangular oil drum, the bottom surface is a cube with a side length of decimeters, and the height is decimeters. How many bottles can be filled into a volumetric 750 ml bottle of such a barrel of oil? ÷=

30 bottles. 2. The waterway from Shanghai to Wuhan is 1100 kilometers. A passenger ship sailed from Shanghai Port to Wuhan Port, the first day traveled the whole 1 5, the second day traveled the remaining 3 4, the third day traveled the remaining 1 2, how many kilometers are left?

Kilometers (kilometers not traveled).

1.Week 3 = 4 9 + 2 9-1 6 = 1 2 km.

2.Work time = 2 3-1 5-3 10 = 1 6 hours.

17 +x=23

x=23-17

x=645 -x=14

x=45-14

x=31x-16 =38

x=38+16

x=54