If a department store sells a commodity with a purchase price of 1980 yuan at 20% of the price, and still makes a profit of 10%, the price of the commodity is () A. 2722.5 yuan B. 2640 yuan C. 2613.6 yuan D. 2160 yuan

If a department store sells a commodity with a purchase price of 1980 yuan at 20% of the price, and still makes a profit of 10%, the price of the commodity is () A. 2722.5 yuan B. 2640 yuan C. 2613.6 yuan D. 2160 yuan

If the bid price is x yuan, the equation can be formulated according to the meaning of the question: 80% · x-1980 = 10% × 1980; the solution is x = 2722.5; so the answer is a

There is a lot of goods in the shopping mall with a price of 12 yuan. A price is 20 and 240 goods are sold every day
There is a batch of goods in the shopping mall with the purchase price of 12 yuan. A sells 240 goods per day at the price of 20 yuan. On the basis of the price of 20 yuan, (1) sell 20 less goods per day when the unit price increases by 1 yuan, (2) sell 40 more goods per day when the unit price decreases by 1 yuan
In order to make a profit of 1920 yuan a day from selling goods, how much is the right price
To list quadratic equations of one variable

(1) If the price is increased by X Yuan, the daily profit will be 1920 yuan
(20+x-12)(240-20x)=1920
The solution is x = 0 or x = 40
That is, the price is 20 yuan, and the profit is 1920 yuan per day
(2) Suppose the price is reduced by Y yuan, and the daily profit is 1920 yuan
(20-y-12)(240+40y)=1920
The solution is y = 0 or y = 2
That is, 20 yuan or 18 yuan can make a profit of 1920 yuan per day

The purchase price of a commodity is 1530 yuan. When it is sold at a 10% discount on the price of the commodity, the profit margin is 15%. How much is the price of the commodity?

Suppose the price of the commodity is x yuan. From the meaning of the question, X × 90% - 1530 = 1530 × 15%. The solution is x = 1955. A: the price of the commodity is 1955 yuan

When a shopping mall sells a commodity, its profit margin increases by 8 percentage points because the purchase price is 6.4% lower than the original purchase price?

Let the original purchase price be a yuan, and the original profit rate of this commodity be X. according to the equation, a (1 + x) − a (1 − 6.4%) a (1 − 6.4%) = x + 8%, and the solution is x = 17%

The sum of the first n terms of the sequence {an} is Sn = 2n + 1-2. The sequence {BN} is an arithmetic sequence with the first term of A1 and the tolerance of D (D ≠ 0), and B1, B3 and B9 are equal proportion sequences. (I) find the general formula of the sequence {an} and {BN}; (II) if CN = 2 (n + 1) BN (n ∈ n *), find the first n terms and TN of the sequence {CN}

(I) because Sn = 2n + 1-2, when n = 1, A1 = S1 = 21 + 1-2 = 2 = 21, when n ≥ 2, an = sn-sn-1 = 2n + 1-2n = 2n, (2 points) A1 = S1 = 21 + 1-2 = 2 = 21, which also satisfies the above formula, so the general formula of the sequence {an} is an = 2n. (3 points) B1 = A1 = 2, if the tolerance is D, then by B1, B3, B9 into the proportional sequence, (2 + 2D) 2 = 2 × (2 + 8D), (4 points) solution, d = 0 (rounding off) or D = 2, (5 points) so the general formula of sequence {BN} is BN = 2n. (6 points) (Ⅱ) CN = 2 (n + 1) BN = 1n (n + 1) (8 points) the sum of the first n terms of sequence {CN}: TN = 11 × 2 + 12 × 3 + 13 × 4 + +1n × (n + 1) (10 points) = 1-12 + 12 − 13 + +1n − 1n + 1 = 1-1n + 1 = NN + 1. (12 points)

An is an equal ratio sequence, the common ratio is 2, if there are two terms am.an Let the root am * an = 4A1 and find the value of M + n. if you want to know how to get it, I'll calculate it all as 4

am=a1*2^(m-1),an=a1*2^(n-1),
√am*an=4a1
Then √ A1 * 2 ^ (m-1) * A1 * 2 ^ (n-1) = 4A1
2^(m+n-2)=16=2^4
m+n-2=4
So m + n = 6

Known sequence {an} satisfies A1 = 1, a (n + 1) = an + (1 / N (n + 1)) (n ∈ n) (1) find A2, A3, A4 (2) infer the general term formula of sequence an and verify it

First question
a2=a1+1/2=1+1/2=3/2
a3=a2+1/6=3/2+1/6=5/3
a4=a3+1/12=5/3+1/12=7/4
Second question
Because a (n + 1) = an + 1 / [n (n + 1)]
So a (n + 1) - an = 1 / n-1 / (n + 1)
a2-a1=1/1-1/2
a3-a2=1/2-1/3
a4-a3=1/3-1/4
…
an-a(n-1)=1/(n-1)-1/n
Add both sides of the above equation
an-a1=1-1/n
an-1=1-1/n
an=2-1/n
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If A4 + A5 + A6 + A7 = 2, A1 × A10 = - 2, then 1 / A4 + 1 / A5 + 1 / A6 + 1 / A7 = ()

According to the condition, we can get A4 * (1 + Q + Q ^ 2 + Q3) = 2, A4 * A4 * q ^ 3 = - 2, then the equation to be solved = (1 / A4) * [1 + Q ^ (- 1) + Q ^ (- 2) + Q ^ (- 3)] = [A4 * (1 + Q + Q ^ 2 + Q3)] / [A4 * A4 * q ^ 3] = - 1
So the final answer is - 1
I hope I can help you

The concept of sequence
Is it necessary to specify the number of A1 in the relation of recurrence formula anan-1?

Of course, or I can't do it

What is the meaning of sequence?

A sequence of numbers arranged in a certain order is called a sequence of numbers. Each number in the sequence is called the item of the sequence. The number in the first place is called the first item of the sequence (usually called the first item), and the number in the second place is called the second item of the sequence The number in the nth place is called this number