Вопрос школьника по предмету Математика
Даша и маша пропалывают грядку за 12 минут, а одна Маша за 20 минут. За сколько минут пропалывает грядку одна Даша?
Ответ учителя по предмету Математика
За целое принимаем всю грядку :
1) 1 : 12 = 1/12 грядки — совместная производительность
2) 1 : 20 = 1/20 грядки — прополет одна Маша за 1 мин.
3) 1/12 — 1/20 = 5/60 — 3/60 = 2/60 = 1/30 грядки — прополет Даша за 1 мин.
4) 1 : 1/30 =
30 мин. — прополет всю грядку одна Даша.
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