Stores a and B sell the same goods at the same price, and they offer different preferential schemes. The goods purchased at point a are charged at 90% of the original price. After purchasing 100 yuan of goods in store B, the goods purchased again are charged at 80% of the original price. How can customers choose the shop to get more preferential treatment?

The first case is: 90% x = 100 + (X-100) 80% x = 200, so when you need 200 yuan to buy goods, you can get the same discount in both stores. The second case is: 90% x > 100 + (X-100) 80% x > 200, so when you need to buy more than 200 yuan, go to store B

How much is 1 * (multiplier) 1 / 2 + 2 * 3 + 3 * 4 + 1 ~ 99 * 100? If we change 99 * 100 to n * (n + 1), what is the result?

1、1/1*2+1/2*3+1/3*4+1/4*5+…… +1/99*100=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+…… +1/99-1/100=1-1/100=99/1002、1/1*2+1/2*3+1/3*4+1/4*5+…… +1/n*(n+1)=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+…… +1/n-1/(n+1)=1-1/(n+1)=...

(1).(x+y)(a+2b) (2).(2a+3)(2/3b+5) (3).(2x+3)(-x-1) (4).(-2m-1)(3m-2) (5).(x-y)^2 (6).(-2x+3)^2

(1).(x+y)(a+2b)
=ax+2bx+ay+2by
(2).(2a+3)(2/3b+5)
=4/3ab+10a+2b+15
(3).(2x+3)(-x-1)
=-2x^2-2x-3x-3
=-2x^2-5x-3
(4).(-2m-1)(3m-2)
=-6m^2+4m-3m+2
=-6m^2+m+2
(5).(x-y)^2
=x^2-2xy+y^2
(6).(-2x+3)^2
=4x^2-12x+9

1. The electric locomotive and the maglev train start from two places 298 km away from each other at the same time. The speed of the maglev train is 20 km / h faster than that of the electric locomotive. Half an hour later, the two trains meet. What is the speed of the two cars? 2. A plane flies between two cities with a wind speed of 24 km / h. It takes 2 hours and 50 minutes to fly along the wind and 3 hours to fly against the wind. The speed of the aircraft and the distance between the two cities are calculated when there is no wind 3. Applied mathematical formula -Which of you is right It's a headache

1. Suppose the speed of electric locomotive is X. the speed of maglev train is 5x + 201 / 2 * (x + 5x + 20) = 2983x + 10 = 2983x = 288x = 96 96200 formula: speed sum = total distance ×encounter time 2. Aircraft speed V km / min 17 / 6 * (V + 24) = 3 * (v-24) 17V + 408 = 18v-432v = 840S = 3 * 816 = 2448

Ask for 30 difficult math problems in junior high school (with complete answers)

1. In order to save energy, a unit shall charge the monthly electricity fee according to the following regulations: if the electricity consumption does not exceed 140 degrees, it will be charged at 0.43 yuan per kilowatt hour; if the electricity consumption exceeds 140 degrees, the excess part shall be charged at 0.57 yuan per hour. If the average electricity charge of a Mexican user in April is 0.5 yuan per kilowatt hour, how much yuan should the user pay in April? The total electricity consumption is set as follows: [(x

The last section of the last sheet - problem solving A commercial building bought Candy A and candy B with 600 yuan. Because the purchase price of candy a was 120% of that of candy B, the weight of candy a returned was 10 kg less than that of candy B (1) If the shopping malls set the sales profit of these two kinds of candy as 10%, what are the selling prices of the two kinds of candy per kilogram respectively? (2) If the two kinds of candies are sold together and the total profit remains unchanged (the same as 1), what is the unit price of the mixed candy? I want the right answer

If the price of a is x kg, then (x + 10) kg 1.2x = x + 10 = x = 50, so the unit price of a is 600 ÷ 50 = 12, and the unit price of B is 600 × (50 + 10) = 10 A's selling price 12 × (1 + 10%) = 13.2 B's selling price 10 × (1 + 10%) = 112 joint profit (13.2-12) × 50 + (11-10) × 60 = 120, total sales 600 + 120 = 720 yuan

One hundred math rational number problems in junior high school Come on, big brothers and sisters

Urgent need for 50 math rational number calculation problems in junior high school

Mixed operation practice of rational number in junior high school
[synchronized training] (45 minutes, Full Score: 100 points)
1. Calculation question: (10 ′× 5 = 50 ′)
（1）3．28-4．76+1 - ；
（2）2．75-2 -3 +1 ；
（3）42÷（-1 ）-1 ÷（-0.125）;
（4）(-48) ÷82-(-25) ÷(-6)2;
（5）- +( )×(-2.4).
2. Calculation question: (10 ′× 5 = 50 ′)
（1）-23÷1 ×（-1 ）2÷（1 ）2；
（2）-14-（2-0.5）× ×[( )2-( )3];
（3）-1 ×[1-3×(- )2]-( )2×(-2)3÷(- )3
（4）(0.12+0.32) ÷ [-22+(-3)2-3 × ];
(5)-6.24×32+31.2×(-2)3+(-0.51) ×624.
[quality optimization training]
1. Fill in the blanks:
(1) If so, then AC 0; if, then AC 0;
(2) If, then ABC =; - a2b2c2 =;
(3) Given that a, B are opposite numbers to each other, C and D are reciprocal to each other, and the absolute value of X is equal to 2, then X2 - (a + b) + CDX =
2. Calculation:
（1）-32-
（2）{1+[ ]×(-2)4}÷(- );
（3）5-3×{-2+4×[-3×(-2)2-(-4) ÷(-1)3]-7}.
[practical application in life]
A bought a hand of stock with 1000 yuan RMB, and then he sold the stock to B with a profit of 10%. Then B sold the stock to a in reverse, but B lost 10%. Finally, a sold the stock to B at 10% of the price sold by B to A. in the above stock transaction ()
A. A is just in balance of loss and profit; B. A makes a profit of 1 yuan;
C. A profit of 9 yuan; D. a loss of 1.1 yuan
Reference answer:
[synchronous training]
1．（1）-0.73 （2）-1 ; （3）-14; （4）- ; （5）-2.9
2．(1)-3 (2)-1 ; (3)- ; (4)1; (5)-624.
[quality optimization training]
(1) >, >; (2) 24, - 576; (3) 2 or 6
[practical use of life] B

A little more It's going to be hard Add or subtract Multiplication and division It's better to have a multiplier Emme, Emme, Emme, EMM, Emme

-5+21*8/2-6-59 68/21-8-11*8+61 -2/9-7/9-56 4.6-(-3/4+1.6-4-3/4) 1/2+3+5/6-7/12 [2/3-4-1/4*(-0.4)]/1/3+2 22+(-4)+(-2)+4*3 -2*8-8*1/2+8/1/8 (2/3+1/2)/(-1/12)*(-12) (-28)/(-6+4)+(-1) 2/(-2)+0/7-(-8)*(-2)...

100 problems of mathematical rational number calculation in junior high school

[-|98|+76+(-87)]*23[56+(-75)-(7)]-(8+4+3)
5+21*8/2-6-59
68/21-8-11*8+61
-2/9-7/9-56
4.6-(-3/4+1.6-4-3/4)
1/2+3+5/6-7/12
[2/3-4-1/4*(-0.4)]/1/3+2
22+(-4)+(-2)+4*3
-2*8-8*1/2+8/1/8
(2/3+1/2)/(-1/12)*(-12)
(-28)/(-6+4)+(-1)
2/(-2)+0/7-(-8)*(-2)
(1/4-5/6+1/3+2/3)/1/2
18-6/(-3)*(-2)
(5+3/8*8/30/(-2)-3
(-84)/2*(-3)/(-6)
1/2*(-4/15)/2/3
-1+2-3+4-5+6-7
-50-28+(-24)-(-22)
-19.8-(-20.3)-(+20.2)-10.8
0.25- +(-1 )-(+3 )
-1-〔1-(1-0.6÷3)〕×〔2-(-3)×(-4)〕
0÷(-4)-42-(-8)÷(-1)3
-32-(-3) 2-(-3)3+(-1)6
3×(-2)2+(-2×3)2+(-2+3)2
(-12)÷4×(-6)÷2
(-12)÷4×(-6)×2
75÷〔138÷（100-54）〕
85×(95－1440÷24)
80400－(4300＋870÷15)
240×78÷（154-115）
1437×27＋27×563
〔75-（12+18）〕÷15
2160÷〔（83-79）×18〕
280＋840÷24×5
325÷13×(266－250)
85×(95－1440÷24)
58870÷(105＋20×2)
1437×27＋27×563
81432÷(13×52＋78)
[37.85-（7.85+6.4）] ×30
156×[(17.7-7.2)÷3]
（947－599）＋76×64
36×(913－276÷23)
-(3.4 1.25×2.4)
0.8×〔15.5-(3.21 5.79)〕
（31.8 3.2×4）÷5
194－64.8÷1.8×0.9 36.72÷4.25×9.9
3.416÷（0.016×35）
0.8×[(10－6.76)÷1.2]
（136+64）×（65-345÷23）
(6.8-6.8×0.55)÷8.5
0.12× 4.8÷0.12×4.8
（58+37）÷（64-9×5）
812-700÷（9+31×11）
（3.2×1.5+2.5）÷1.6
85+14×（14+208÷26）
120-36×4÷18+35
（284+16）×（512-8208÷18）
9.72×1.6-18.305÷7
4/7÷[1/3×（3/5-3/10）]
（4/5+1/4）÷7/3+7/10
12.78－0÷（ 13.4＋156.6 ）
37.812-700÷（9+31×11）
（136+64）×（65-345÷23）
3.2×（1.5+2.5）÷1.6
85+14×（14+208÷26）
（58+37）÷（64-9×5）
(6.8-6.8×0.55)÷8.5
（284+16）×（512-8208÷18）
0.12× 4.8÷0.12×4.8
（3.2×1.5+2.5）÷1.6
120-36×4÷18+35
10.15-10.75×0.4-5.7
5.8×（3.87-0.13）
+4.2×3.74 347+45×2-4160÷52
32.52-（6+9.728÷3.2）×2.5 87（58+37）÷（64-9×5）
[（7.1-5.6）×0.9-1.15] ÷2.5 （3.2×1.5+2.5）÷1.6
5.4÷[2.6×（3.7-2.9）+0.62] 12×6÷（12-7.2）-6
3.2×6+（1.5+2.5）÷1.6 （3.2×1.5+2.5）÷1.6
5.8×（3.87-0.13）+4.2×3.74
33.02－（148.4－90.85）÷2.5