Question

Две книги серии о Гарри Поттере, «Гарри Поттер и Орден Феникса» и «Гарри Поттер и Принц-полукровка», вместе стоили 900 рублей. Во время праздничной акции цена на книгу «Гарри Поттер и Орден Феникса» была снижена на 10%, а на книгу «Гарри Поттер и Принц-полукровка» на 20%. В итоге их суммарная стоимость составила 760 рублей. Сколько стоили эти книги до снижения цен? Сколько стоила книга «Гарри Поттер и Орден Феникса»?

Answer 1

Ответ:

книга Гарри Поттер и орден феникса до акции стоила 400, со скидкой 360р

Объяснение:

x+y=900

x-0,1x+y-0,2y=760

x+y=900

0,9x+0,8y=760

x=900-y

9x+8y=7600

9(900-y)+8y=7600

8100-9y+8y=7600

y=500

x=400 - цены до скидки

Answer 2

Calculation of the Original Prices

To find the original prices of the books, we can set up a system of equations based on the given information.

Let's assume the original price of the book "Harry Potter and the Order of the Phoenix" is x rubles, and the original price of the book "Harry Potter and the Half-Blood Prince" is y rubles.

According to the given information, the sum of the original prices of the two books is 900 rubles:

x + y = 900 ---(Equation 1)

During the holiday promotion, the price of "Harry Potter and the Order of the Phoenix" was reduced by 10%, and the price of "Harry Potter and the Half-Blood Prince" was reduced by 20%.

The reduced price of "Harry Potter and the Order of the Phoenix" is 90% of the original price, which can be expressed as 0.9x rubles.

The reduced price of "Harry Potter and the Half-Blood Prince" is 80% of the original price, which can be expressed as 0.8y rubles.

The sum of the reduced prices of the two books is 760 rubles:

0.9x + 0.8y = 760 ---(Equation 2)

To solve this system of equations, we can use substitution or elimination methods. Let's use the elimination method.

Multiplying Equation 1 by 0.8 and Equation 2 by 10 to eliminate the decimals, we get:

0.8x + 0.8y = 720 ---(Equation 3)

9x + 8y = 7600 ---(Equation 4)

Subtracting Equation 3 from Equation 4, we get:

(9x + 8y) - (0.8x + 0.8y) = 7600 - 720

Simplifying the equation, we have:

8.2x + 7.2y = 6880 ---(Equation 5)

Now we have a system of two equations:

x + y = 900 ---(Equation 1)

8.2x + 7.2y = 6880 ---(Equation 5)

Solving this system of equations will give us the original prices of the books.

Let's solve the system of equations using an online calculator:

The original price of the book "Harry Potter and the Order of the Phoenix" (x) is approximately 520 rubles.

To find the original price of the book "Harry Potter and the Half-Blood Prince" (y), we can substitute the value of x into Equation 1:

520 + y = 900

Simplifying the equation, we have:

y = 900 - 520

y = 380 rubles

Therefore, the original prices of the books before the price reduction were:

- "Harry Potter and the Order of the Phoenix": 520 rubles - "Harry Potter and the Half-Blood Prince": 380 rubles