7th Grade Mathematics Summer Vacation Big Tandem Northern Women and Children s Press, Revised Editi

If the distance between AC and AC is x kilometers, then the car departs to C and then returns to meet Group A after 2x (60+4)=x 32 hours, then there is x 32+(18-4*x 32) 60=x 60+(18-x) 4

If x=16, the distance between AC and the two places is 16 km.

Group A walked 4*16 32 2 km, and Group B walked 18-16 2 km.

Solution: Suppose soap is $ x and toothpaste is $ y.

39x+21y=396

52x+28y=518

13x+ because 132 ≠

So there is no solution to the equation.

So there is a mistake. I'm a teacher, thank you.

It is known that in the solution of the binary equation 3x+2y=k, 2x+3y=k+3, the sum of x,y is 8, and the value of k is obtained.

Solution: Replace 3x+2y=k with 2x+3y=k+3 to get:

2x+3y=3x+2y+3

Shift: 2x+3y-3x-2y=3

Merge similar items: carry filial piety y-x=3

x+y=8y-x=3

x+y=8+y-x=3:

2y=11y=

Substituting y==y-x=3 to get the back draft.

x=I'm a teacher, thank you.

Solution: 12+b=-2

5a+20=15②

Derived: b=10

Result: a=-1

So get it again:

x+5y=15③

4x-y=-2

Solution: Hall do x=14, y=29 5

I'm a teacher, thank you.

At this time, the total profit w 20x+16800-a*x=(20-a)x+16800, a<200-170 30

When A<=20, X takes the maximum value, that is, X 40 (i.e., Type A is all sold by A, the same as Q2).

When A>20, X takes the minimum value, i.e., X 10 (i.e., B sells Type A).

Input: 2013 Summer Vacation Seventh-Grade Mathematics You can check and learn to carry a boat.

Is it applicable to people's education textbooks?

1) Set up a closed water pipe before the land mold cover put x hours of yards of water.

The water released within 2 hours after the water pipe is closed accounts for a pool of water

There was one in the pool before. of water. x=

Wasted : pool).

2) After Y hours, the water in the pool begins to overflow and make a morning noise. y=

1) Set the water for x hours before closing the water pipe.

The water released within 2 hours after the water pipe is closed accounts for a pool of water

There was water in the pool before.

x= wasted: pool).

2) The water in the pool begins to overflow after Y hours. y=