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Теория: Умножение двузначных чисел

Задание

Перемножить числа:

 \(\displaystyle \times\)\(\displaystyle 2\)\(\displaystyle 5\)
 \(\displaystyle 3\)\(\displaystyle 1\)
\(\displaystyle +\) 
 
 

 

Решение

1. Умножаем единицы числа \(\displaystyle 3\underline{1} \) (это цифра \(\displaystyle 1 \)) на число \(\displaystyle 25{\small : }\)

 

\(\displaystyle 1 \cdot 25=25 {\small . }\)

 

 \(\displaystyle \times\)\(\displaystyle \bf 2\)\(\displaystyle \bf 5\)
 \(\displaystyle 3\)\(\displaystyle \bf 1\)
\(\displaystyle +\) \(\displaystyle \bf 2\)\(\displaystyle \bf 5\)
\(\displaystyle ?\)\(\displaystyle ?\)  
 \(\displaystyle ?\)\(\displaystyle ?\)\(\displaystyle ?\)

 

2. Умножаем десятки числа \(\displaystyle \underline{3}1\) (это цифра \(\displaystyle 3 \)) на число \(\displaystyle 25{\small : }\)

 

\(\displaystyle 3 \cdot 25=75 {\small . }\)

 

 \(\displaystyle \times\)\(\displaystyle \bf 2\)\(\displaystyle \bf 5\)
 \(\displaystyle \bf 3\)\(\displaystyle 1\)
\(\displaystyle +\) \(\displaystyle 2\)\(\displaystyle 5\)
\(\displaystyle \bf 7\)\(\displaystyle \bf 5\) 
 \(\displaystyle ?\)\(\displaystyle ?\)\(\displaystyle ?\)

 

3. Складываем числа:

\(\displaystyle +\) \(\displaystyle 2\)\(\displaystyle 5\)
\(\displaystyle 7\)\(\displaystyle 5\)  
 \(\displaystyle 7\)\(\displaystyle 7\)\(\displaystyle 5\)

 

В итоге мы получаем:

 \(\displaystyle \times\)\(\displaystyle 2\)\(\displaystyle 5\)
 \(\displaystyle 3\)\(\displaystyle 1\)
\(\displaystyle +\) \(\displaystyle 2\)\(\displaystyle 5\)
\(\displaystyle 7\)\(\displaystyle 5\)  
 \(\displaystyle 7\)\(\displaystyle 7\)\(\displaystyle 5\)

Ответ: \(\displaystyle 775 {\small . }\)