Xiaoming and I want to buy a toy car for 28 yuan, so each person should pay 14 yuan, but I have no money, so I borrow 14 yuan from Xiaohua (Xiaohua also wants it, so he agrees to buy a toy car with me for 7 yuan, but Xiaohua gives it all). How much money should I pay back to Xiaohua?

It's 14 yuan

A math problem about borrowing money
A borrows 500 yuan from B and C, which is 1000 yuan in total. Then he buys 970 items, and the rest is 30 yuan. Then he returns 10 yuan to each person, and the rest is 10 yuan. Now he owes 490 yuan to B and C, which is 980 yuan in total. A only has 10 yuan on him, which is 990 yuan in total. Where is the remaining 10 yuan?

A borrows 500 yuan from B and C, which is 1000 yuan in total. Then he buys 970 items, and the rest is 30 yuan. Then he gives back 10 yuan to each person, and the rest is 10 yuan. Now he owes 490 yuan to B and C, which is 980 yuan in total. A has only 10 yuan {990 yuan in total, so where is the remaining 10 yuan}}
Money owed 980
It cost 970
10 left
just right

Four and a half hours later, the distance between the two vehicles was 55 thousand kilometers
M. the speed of passenger cars is one third faster than that of freight cars. What is the speed of passenger cars and freight cars?

Suppose: the speed of freight car is 3x, then the speed of passenger car is 4x
4.5（3x+4x）=1000-55
7x=210
X = 30 hours
The speed of freight cars is 90, and that of passenger cars is 120

3a^3a^3+a^2a^4-4aa^2a^3

Solution
3a³a³+2a²a^4-4a×a²×a³
=3a^6+2a^6-4a^6
=(3+2-4)a^6
=a^6

The truck runs 75 kilometers in 1.5 hours and the bus 112.5 kilometers. Use 2.5 hours to calculate the time ratio and speed ratio of the truck and bus
Process?

75 △ 1.5 = 50 km 112.5 △ 2.5 = 45 km 50 to 45 km

Given that the sum of the monomial 6x ^ m + 1y ^ 2m-3 and 2 / 3x ^ 7-2my-1-2n is a monomial, then 2 + Mn=---

The sum of the binomial 6x ^ m + 1y ^ 2m-3 and 2 / 3x ^ 7-2my-1-2n is a binomial
∴m+1=7-2m 2m-3=-1-2n
m=2 n=-1
2+mn=2+1*(-2)=2-2=0

There are 240 tons of cement on the construction site, 3 / 8 of which were used in the first time and 1 / 6 in the second time. How many tons were used in the two times?

240x (3 / 8) = 90 for the first time
240-90 = 150 left
150x (1 / 6) = 25 for the second time
Two times, a total of 90 + 25 = 115

We know the quadratic equation AX2 + x-a = 0 (a ≠ 0) about X, and prove that for any non-zero real number a, the equation always has two real roots with different signs

It is proved that: ∵ △ = 12-4a × (- a) = 1 + 4a2 ＞ 0, for any nonzero real number a, the equation always has two real roots with different signs

A pile of yellow sand is transported 25% in the first day, 4 tons less than in the second day. At this time, 56 tons are left. How many tons of yellow sand are there?

(56 + 4) △ 1 - (25% + 25%), = 60 △ 1-50%, = 60 △ 50%, = 120 tons; a: this pair of yellow sand is 120 tons in total

If LGA and LGB are two of the equations 2x-4x + 1 = 0, find the value of LG (A / b),

LGA and LGB are two different real roots of the equation 2x ^ 2-4x + 1 = 0. According to Weida's theorem LGA + LGB = 2 lgalgb = 1 / 2 LG (B / a) ^ 2 = 2lg (B / a) = 2 (LGB LGA) | LGB LGA | ^ 2 = (LGB + LGA) ^ 2-4lgalgb = 4-4 * (1 / 2) = 2 LGB LGA = ± √ 2, then LG (B / a) ^ 2 = ± 2 √ 2

Xiaoming and I want to buy a toy car for 28 yuan, so each person should pay 14 yuan, but I have no money, so I borrow 14 yuan from Xiaohua (Xiaohua also wants it, so he agrees to buy a toy car with me for 7 yuan, but Xiaohua gives it all). How much money should I pay back to Xiaohua?