The stationery store bought 100 pens at the price of 4 yuan each, and each pen was sold at 6 yuan. When some pens were sold, the remaining pens were sold at a 10% discount. When all pens were sold, the store made a total profit of 188 yuan. How many pens were sold at a 10% discount? Don't use the equation, but use the formula

A stationery shop bought pens at the price of a (a is a positive integer) yuan and decided to increase the price by 2 yuan for each pen. When checking out, it found that the total sales of pens was (399a + 805) yuan. How many pens were purchased and how much was the purchase price of each pen

Purchase x pens;
(a+2)x=399a+805;
x=(399a+805)/(a+2)
=[399(a+2)+7]/(a+2)
=399+7/(a+2)
If 7 / (a + 2) is a positive integer, only a + 2 = 7, that is, a = 5; X = 399 + 1 = 400
So I bought 400 pens, and the price of each pen was 5 yuan

A stationery shop bought a batch of pens at the price of 10 yuan each, and then sold them at a fixed price with 40% profit
When three fourths of these pens are sold, they have made a profit of 240 yuan. How many pens are there in total?

14x3 / 4x = 10x + 240, the final result is x = 480. A total of 480 pens in this batch

If the area of a circle is equal to that of a square, their circumference must also be equal______ (judge right or wrong)

Let the area be 12.56, 12.56 ≈ 3.5 × 3.5, the perimeter of the square be 3.5 × 4 = 14, π R2 = 12.56, & nbsp; R2 = 4, & nbsp; r = 2, the perimeter of the circle be 2 π r = 2 × 3.14 × 2 = 12.56, so the answer is wrong

If the x power of a = the Y power of B = the Z power of 2001, (a, B are positive integers) and 1 / x + 1 / y = 1 / Z, find the value of a + B
I didn't learn logarithm

X power of a = y power of B = Z power of 2001
Taking logarithm, we get xlna = ylnb = zln2001
1/x+1/y=1/z
lna/zln2001+lnb/zln2001=1/z
lna+lnb=ln2001
I can't do it

May I ask how many five digit numbers of at least one digit 3, which is a multiple of 3, will appear?

There are a total of 99999-9999 = 90000 (digits); among them, there are 30000 multiples of 3; 8 × 9 × 9 × 3 = 17496 (digits); 30000-17496 = 12504 (digits); a: there are 12504 five digits with a number of 3 and multiples of 3

Calculate the surface area and volume of the following figure. (unit: cm)

Surface area: (6 * 10 + 4 * 10 + 6 * 4) * 2-2 * 2 * 2 = 240 square cm
Volume: (4 * 6-2 * 2) * 10 = 200 cc
If it helps you, please take it. Thank you
This is the first answer. I wish you progress!

What is the nearest day for the earth to the sun

At the beginning of January every year, the earth is at the perihelion of the orbit around the sun, and the distance between the sun and the earth reaches the minimum value, about 147.1 million kilometers

Help me solve some practical problems in junior high school
1. The basic price of domestic electricity in a bureau is 0.40 yuan. If the monthly electricity consumption exceeds a degree, 70% of the basic electricity price will be charged for the excess
(1) A household uses 84 degrees of electricity in May, and calculates a value by paying 30.72 yuan
(2) If the average electricity charge of the user in June is 0.36 yuan per kilowatt hour, how many kilowatt hours of electricity consumption and how much yuan should be paid in June?
2. A man walked 3 kilometers from his home to the bus station in the first hour. He looked at his watch and estimated that the speed would be 40 minutes late, so he walked the rest of the way at the speed of 4 kilometers per hour. Instead, he arrived 45 minutes ahead of time, and asked for the distance from the other person to the bus station
3. For a project, it will take 10 days, 12 days and 15 days for Party A, Party B and Party C to do it alone. Now it is planned to start the project in 7 days, and Party B and Party C will cooperate for 3 days. Can party A and Party C cooperate to complete the project as planned?

1 (1).0.4A +0.4*70%(84-A) = 30.72
The solution is: x = 60
(2) Let's use x degrees in June
0.4 * 60 + 0.4*70 *(x-60) = 0.36x
The solution is: x = 90
2. The planned time from home to the station is x hours
Then: 3 (x + 2 / 3) = 4 (x-1-3 / 4) + 3
The solution is: x = 6
So the distance = 3 (x + 2 / 3) = 20km
3. After 3 days of cooperation, the remaining work is
1-（1/12+1/15）* 3 =11/20
It will take (11 / 20) / (1 / 10 + 1 / 15) = 3.3 days
3+3.3

After a parallelogram is cut and complemented, it is a square. The perimeter of the square is 16 cm. The area of the parallelogram is______ Square centimeter

16 △ 4 = 4 (CM), 4 × 4 = 16 (cm 2). Answer: the area of parallelogram is 16 cm 2