На склад поступило 2 партии изделий: первая – 4000 штук, вторая – 6000 штук. Средний процент нестандартных изделий в первой партии 20%, во второй – 10%. Наудачу взятое со склада изделие оказалось нестандартным. Найти вероятность того, что оно: а) из первой партии, б) из второй партии.​

1)the two friends lived in liverpool, didn't they? 2)the boys didn't like doing sums, did they? 3)the river mersey was far busier in the old days, wasn't it? 4)the narrator's relatives had seen a lot of parts of the globe, hadn't they? 5)the boys were not teenagers at the time, were they? 6)the boys tried to plan their voyage, didn't they? 7)the boys didn't prepare food and drink for their voyage, did they? 8)the boys could easily get on board the ship, couldn't they? 9)the boys had to give themselves up after midge got sick, didn't they? 10)the narrator's parents didn't believe his story, did they?

Обозначим первоначальное количество - Х.

Тогда можно записать два уравнения.

1) х + а = 1/8*V

2) x - a = 3/20*V

Решаем систему уравнений.

Сложим два уравнения и получим 3)

3) 2*x = (1/8 + 3/20)*V = 11/40*V

Находим неизвестное - Х

4) X = 11/40 : 2 = 11/80 - было - ОТВЕТ

Вычтем уравнения - 1) - 2) = 5)

5) 2*а = (1/8 -3/20)*V = - 1/40

Находим неизвестное - а

6) a = 1/40 : 2 = -1/80  - изменение - ОТВЕТ

ПРОВЕРКА

11/80 + (- 1/80) = 10/80 = 1/8 - правильно

11/80 + 1/80 = 12/80 = 3/20 - правильно

Дополнительно

а - отрицательное число.  

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