Master Zhang bought three apples at 1 yuan and sold them at 2 yuan and 5 apples. How many apples must he sell to make a profit of 10 yuan?

Master Zhang bought three apples at 1 yuan and sold them at 2 yuan and 5 apples. How many apples must he sell to make a profit of 10 yuan?

150 10 / (2 / 5-1 / 3) = 150

Li bought 3kg of apples and 3kg of pears, which cost 16.5 yuan. Wang bought 2kg of apples and 4kg of pears, which cost 17 yuan. How many yuan per kilogram of apples

16.5 △ 3 = 5.5 (yuan)
17-16.5 = 0.5 yuan
5-0.5 △ 2 = 2.5 (yuan) apple
Answer: Apple 2.5 yuan

Is it necessary to list several equations when there are several unknowns?

This is usually the case. Only in this way can we find the unique root
But there are some special exceptions, such as: (x-1) ^ 2 + (Y-2) ^ 2 = 0

Why does the contact area have nothing to do with the friction? Doesn't the contact area determine the pressure?
RT
Don't answer that the friction force is determined by the roughness and pressure of the object, which everyone knows
In the afternoon, when doing the experiment in the experimental class, the contact area is different and the friction force is also different. But the teacher said clearly that the friction force of the contact area has nothing to do with it
But the contact area determines the pressure, so it also determines the pressure, so isn't that relevant?

For a given object, its gravity is certain. If it is placed on a horizontal table, the pressure is certain. The pressure of the object on the table is also determined by the contact area between the object and the contact surface. As for the experiment you do, it should be caused by the different roughness of different parts of the object, or there may be a large error in the experiment

Solving the problem of mathematical function in Senior One: given f (x) = 2x-1, G (x) = {x square, X is greater than or equal to 0; - 1, X is less than 0} find f [g (x)]
Speed, solve!

The problem is the complex function of piecewise function
Take the range of G (x) as a domain of F (x)
Because the problem f (x) = 2x-1, there is no requirement to define the field, just need to substitute g (x)
f(x)=2x^2 (x>=0)
=-3 (x

A passenger car and a freight car run opposite each other. The passenger car runs 1.4 kilometers per minute, and the freight car runs 0.85 kilometers per minute. The bus body is 600 meters long, and the freight car body is 1200 meters long. How many minutes does it take from two cars meeting to two cars leaving?

600 + 1200 = 1800 (m) = 1.8 (km), 1.8 △ 1.4 + 0.85 = 1.8 △ 2.25, = 0.8 (min); a: it needs 0.8

Given the set a = (1,2) B = (2,3), what is the intersection of a and B equal to

(2)

Factorization (formula method): A ^ 2 + 5A + 6 (process)

a²+5a+6
= a²+2a+3a+6
=a（a+2）+3×（a+2）
=（a+3）（a+2）

The fruit shop shipped 630kg of oranges, apples and pears. The mass ratio of oranges and pears is 5:6, and pears is 35 times that of apples. How many kg of each of the three kinds of fruits?

From the analysis, we know that: the mass ratio of orange, pear and apple is 5:6:10, orange is 630 ^ (5 + 6 + 10) × 5, = 630 ^ (21 × 5, = 30 × 5, = 150 (kg); pear is 630 ^ (5 + 6 + 10) × 6, = 630 ^ (21 × 6, = 30 × 6, = 180 (kg); apple is 630 ^ (5 + 6 + 10) × 10, = 630 ^ (21 × 10, = 30 × 10, = 300 (kg); answer: orange is 150 kg, pear is 180 kg, apple is 180 kg The fruit is 300 kg

Fill the bottle with a bottle of water, pour out 12% of all the water, then pour in the same amount of alcohol, pour out 13% of all the solution, fill it with alcohol, then pour out 14% of all the solution, and fill it with alcohol, then the alcohol accounts for 30% of all the solution______ %．

1-12 = 12; 12 × (1-13) = 13; 13 × (1-14) = 14; 1-14 = 34.34 × 100% = 75%