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3'''A is A, B is B, C is C, and the difference between each and 6 yuan is calculated first.

A yuan B yuan. C 8-6 2 yuan.

Based on the total difference between equals, the column equation is.

18a 12b＝20c

9a 6b＝10c

Knowing that c is a multiple of 3, you may wish to set c 3

then 9a 6b 30

3a 2b＝10

can be set a 2, b 2, and the equation holds.

i.e. a:b:c 2:2:3

Since the value of abc is only one of the eligible ones, other answers can be obtained.

For example, a:b:c 6:1:6

Check: 8 6 78 yuan.

78 (6 1 6) $6.

Then you add that ratio to the answer to the question below.

1: When A reaches the end point, B is 20 meters behind A, indicating that the velocity ratio of A and B is 100 to (100-20) = 5 to 4

If the speed of A and B remains the same, and in order for A and B to reach the end at the same time, the time required by B is 100 4 = 25, then A can run 5 * 25 = 125 meters, so the starting line of A should move backward by 125-100 = 25 meters than the original.

2: S A S is equal to 7 6, T A T is equal to 9 10V, A V is equal to 21 20

1.You can calculate it like this: if you understand x of one type, y of two kinds, and 50 of three types, then x+y=100-50 (person).

and x+2y+3*50=75+83+65, that is, x+2y=73 (person-time) solution: y=23

The key to this is to change the concept of how many people to how many "person-times", if one person understands one, it is considered 1 person-time, if it understands two, it is 2 people, and so on.

2.This is a matter of common divisor, first look at the number divisible by 3: 1000 3 = 333 (pcs).

Then calculate the ones that can be divisible by 3 and 7: 1000 (3*7)=47 (pieces) then divisible by 3 and not divisible by 7 is: 333-47=2863Again, if only one of the proficient is x, and the two proficient are y, then there is:

x+y=100%-10%=90%

Again: x+2y=70%+80%=150%.

Solution: y=60%.

4.Let only one have x, two participants are y, and the rest are non-participants.

Yes: x+2y=1 3+40%.

y=2/15

Solution: x=7 15

Then the non-participating = 1-7 15-2 15 = 6 15 = 40% 5Suppose there are x people who only participate in one of the two items, and y people who participate in two items:

x+2y=18+24=42

y=6 solution: x=30

Total number of people = x + y + 13 = 30 + 6 + 13 = 496Well, this question is to subtract the multiple of 3, and then subtract the multiple of 5. But since some numbers are multiples of 3 and 5, this will subtract some more, which is a multiple of 3*5=15, and then add it.

Between 300 and 500 there are 199 numbers.

Multiples of 3: 199 3=66

Multiples of 5: 199 5=19

Multiples of 15: 199 15 = 13

So: what you ask for = 199-66-19 + 13 = 127

Move the image of the function y=ax 2+bx+c down by 3 units.

In the image of the function y=ax 2+bx+c-3, consider that the number of intersections between this function and the horizontal axis is the number of nuclei of the root.

If the question is correct, it is two roots with the same number or the same positive or no solution.

If the ordinate of the vertex of the problem is 3, then the close touch is an equal positive follow.

Solution: The cross-sectional area of the cuboid timber is:

The volume of the box wood is:

Increase the surface area by 2 per truncation 1.

Because (1+2+..n-1))/n=[n(n-1)/2]/n=(n-1)/2

So 1+1 2+(1 nuclear shed 3+2 change to 3)+(1 4+2 4+3 4)+1/50+2/50+..49/50)

1+1 2+2 and Spike 2+...49/2=1+(1+2+3+..49)/2

1+49*50/2*1/2 (1+2+……n=n(n+1)/2)=1+1225/2

The second question is not clear, let's make it clearer. Content under the root number.

Hope it helps!

+|, squared of the root number (a-3).b-1|=0

The sum of squares and absolute values is non-negative, so if a 3 b 1 is a waist, 1+1<3 cannot be a triangle.

So a is for the waist.

The circumference is 3+3+1 7

I hope the explanation is clear enough

628 radius.

Area = square of the radius