Question

Учитель купил 4 ручки.Без первой ручки он отдал 80 рублей. Без второй - 84 руб.Без третьей -90 и без четвертой - 94.Какая из 4-х ручек самая дорогая? Сколько стоит самая дорогая ручка?

Answer 1

Пусть а рублей стоит 1 ручка

б рублей - вторая

с рублей - третья

д рублей - четвертая

б+с+д=80   => б=80-с-д

а+с+д=84   =>а=84-с-д

а+б+д=90   =>д=90-а-б

а+б+с=94    =>с=94-а-б

Подставим

б=80-94+а+б-90+а+б

б=104-2*а

Подставим в д

д=90-а-104+2*а

д=а-14

Подставим в с

с=94-а-104+2*а

с=а-10

Подставим в а

а=84-а+10-а+14

3*а=108

а=36 руб - 1ручка

б=104-72=32 руб - 2 ручка

с=36-10=26руб - 3 ручка

д=36-14=22 руб - 4 ручка

Ответ самая дорогая первая ручка стоит 36 рублей

Answer 2

Problem Analysis

To determine which of the four pens is the most expensive and the price of the most expensive pen, we need to analyze the given information. The teacher bought four pens and the prices of the pens without the first, second, third, and fourth pens are 80 rubles, 84 rubles, 90 rubles, and 94 rubles, respectively.

Solution

To find the most expensive pen, we need to compare the prices of the pens. Let's analyze the prices:

- The price without the first pen is 80 rubles. - The price without the second pen is 84 rubles. - The price without the third pen is 90 rubles. - The price without the fourth pen is 94 rubles.

From the given information, we can see that the price of each pen increases by 4 rubles. Therefore, the first pen is the cheapest, the second pen is slightly more expensive, the third pen is even more expensive, and the fourth pen is the most expensive.

So, the fourth pen is the most expensive pen.

To find the price of the most expensive pen, we can add the price difference between each pen. Starting from the price without the first pen (80 rubles), we can add 4 rubles for each subsequent pen:

- Price without the first pen: 80 rubles - Price without the second pen: 80 rubles + 4 rubles = 84 rubles - Price without the third pen: 84 rubles + 4 rubles = 88 rubles - Price without the fourth pen: 88 rubles + 4 rubles = 92 rubles

Therefore, the price of the most expensive pen is 92 rubles.

Conclusion

The fourth pen is the most expensive pen, and its price is 92 rubles.

Please let me know if there is anything else I can help you with.