Math problems no, help!! ）

1. x+y=300

60%x+90%y=300*70%

2.Let the velocity of A be x m min and the velocity of B be y m min.

30x=30y+300

2x+2y=300

Solution: x=80 y=70

The speed of A is 80 meters, and the speed of B is 70 meters.

3.Set: The length of the train body is x meters, and the speed is y meters and seconds.

60y=1000+x

40y=1000-x

Solution: x=200 y=20

The total length of the train body is 200 meters, and the speed is 20 meters per second.

1. One element quadratic (1) x + y = 300 (2) 90% y + 60% x = 3002, the speed of set A x meters per minute, the speed of B y meters per minute (1) 300 (x-y) = 30 (2) 300 (x+y) = 2 so can be connected x80 y = 70

Set: The length of the train body is x meters, and the speed is y meters and seconds. （1）60y=1000+x2）40y=1000-x

Solution: x=200 y=20 played so hard, one.

Answer: The 9 yuan spent per person already includes the 2 yuan hidden by the waiter (i.e. ***25 yuan + 2 yuan hidden by the waiter = 27 yuan = 3 * 9 yuan) Therefore, when calculating the composition of the 30 yuan, the 2 yuan hidden by the waiter should not be counted, but the 1 yuan returned to each person should be added. Namely:

3 * 9 + 3 * 1 = 30 yuan is just right! Think about it another way. The three people paid a total of 30 yuan, spent 25 yuan, and the waiter hid 2 yuan, so each person spent 9 yuan, plus the 1 yuan they shared, it was exactly 30 yuan.

So the dollar was found.

Summary: This question confuses people mainly because it separates the 2 yuan from the 27 yuan, and the algorithm of the original question mistakenly believes that the 2 yuan left by the waiter is not included in the 27 yuan, so there is an error result of 1 yuan less; In fact, the 2 yuan left without permission was included in the 27 yuan, plus the 3 yuan returned, and the result was exactly 30 yuan.

If you think about it, it should be like this: at the beginning, each person paid ten yuan, a total of thirty yuan. The boss returned 5 yuan, 30 minus 25 = 5 yuan, and the waiter kept 2 yuan, that is to say, he also paid 3 yuan, 30-5 + 3 = 28 28 + 2 = 30

Originally, the accommodation was only 25 yuan, because the waiter swallowed 2 yuan, the three spent 27 yuan, and the other 3 yuan was the boss's preferential rebate. Therefore, the original formula should be 3 x 9 = 27 yuan (including 2 yuan hidden by the waiter) = 30 yuan 3 yuan preferential rebate.

What kind of dollar, what are you talking about? Obviously, that's not the case at all!

Expenditure: (10 + 10 + 10) -3 = 27 yuan Rent: 25 yuan.

Service: 2 RMB.

What's the dollar?

The 27 yuan includes the waiter's hidden 2 yuan.

In this way, at the beginning, each person paid 10 yuan, and now it is returned 1 yuan, that is, 10-1=9, and each person only spent 9 yuan.

30 yuan was originally in the boss's place, but the boss returned 5 yuan, this 5 yuan = the money in the hands of three people + the waiter's money;

30 yuan = the boss's money + the money in the hands of three people + the waiter's money;

Money spent by three people = money from the boss + money from the waiter.

The above relationship is correct.

Let the radius be r, then the circumference of the semicircle = 2r + r =

then r = 20 cm.

The area of the circle is: r = square centimeter.

The semicircle is 1256 2 = 628

Let the radius of the circle be r centimeters.

r = square centimeter.

1.Set up x acres of eggplant. 1700x+1800(25-x)=44000 x=10 Tomatoes: 25-10=15 acres.

Profit 10 * (2400-1700) + 15 * (2600-1800) = 19000 yuan.

2.No.

4 Price 510*(1-4%)=Yuan (510-400) 400*100%= (1+10%)m= Price Reduction Give a little bit of points- -Do it to death.

Let the radius r of the circle, since the sum of the two long sides of this rectangle is approximately the circumference of the circle, the equation is obtained:

2 solution: r=2

The area of the circle: s = square centimeters).

Let the speed be v and the time for the motorcycle to catch up with the bike is t

then v(1+t)=50t

v（1+2t）=120

Solving this system of equations gives v=30 t=

So the speed of the bike is 30 kilometers per hour.

Suppose the postman rides a bicycle at a speed of x

120-1*x) 2x=[(120-1*x) 2+1*x] 50x1=30 x2=-285 (rounding).

The speed of the postman on a bicycle is 30 kilometers per hour.

1*x is an hour's journey by bicycle.

120-1*x) 2 is the distance traveled after getting the mail divided by x is the time taken.

120-1*x) 2+1*x is the return (or delivery) distance traveled by the motorcycle, divided by 50, which is the time taken.