Question

90*79,597

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Gene

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96 Answers

For convenience, place the longer number on top
$7957\times 90$

Line up the numbers
$\begin{matrix}\:\:&7&9&5&7\\\times &\:\:&\:\:&9&0\end{matrix}$

Multiply the top number by the bolded digit of the bottom number
$\begin{matrix}\:\:&\bold{7}&\bold{9}&\bold{5}&\bold{7}\\\times &\:\:&\:\:&9&\bold{0}\end{matrix}$

Mutliply the bold numbers $7\times 0=0$
$\frac{\begin{matrix}\:\:&7&9&5&\bold{7}\\\times &\:\:&\:\:&9&\bold{0}\end{matrix}}{\begin{matrix}\:\:&\:\:&\:\:&\:\:&0\end{matrix}}$

Mutliply the bold numbers $5\times 0=0$
$\frac{\begin{matrix}\:\:&7&9&\bold{5}&7\\\times &\:\:&\:\:&9&\bold{0}\end{matrix}}{\begin{matrix}\:\:&\:\:&\:\:&0&0\end{matrix}}$

Mutliply the bold numbers $9\times 0=0$
$\frac{\begin{matrix}\:\:&7&\bold{9}&5&7\\\times &\:\:&\:\:&9&\bold{0}\end{matrix}}{\begin{matrix}\:\:&\:\:&0&0&0\end{matrix}}$

Mutliply the bold numbers $7\times 0=0$
$\frac{\begin{matrix}\:\:&\bold{7}&9&5&7\\\times &\:\:&\:\:&9&\bold{0}\end{matrix}}{\begin{matrix}\:\:&0&0&0&0\end{matrix}}$

Multiply the top number by the bolded digit of the bottom number
$\frac{\begin{matrix}\:\:&\bold{7}&\bold{9}&\bold{5}&\bold{7}\\\times &\:\:&\:\:&\bold{9}&0\end{matrix}}{\begin{matrix}\:\:&0&0&0&0\end{matrix}}$

Mutliply the bold numbers $7\times 9=63$
$\frac{\begin{matrix}\:\:&\:\:&\:\:&\:\:&6&\:\:\\\:\:&\:\:&7&9&5&\bold{7}\\\:\:&\times &\:\:&\:\:&\bold{9}&0\end{matrix}}{\begin{matrix}\:\:&\:\:&0&0&0&0\\\:\:&\:\:&\:\:&\:\:&3&\:\:\end{matrix}}$

Add the carried number to the multiplication $6+5\times 9=51$
$\frac{\begin{matrix}\:\:&\:\:&\:\:&5&\bold{6}&\:\:\\\:\:&\:\:&7&9&\bold{5}&7\\\:\:&\times &\:\:&\:\:&\bold{9}&0\end{matrix}}{\begin{matrix}\:\:&\:\:&0&0&0&0\\\:\:&\:\:&\:\:&1&3&\:\:\end{matrix}}$

Add the carried number to the multiplication $5+9\times 9=86$
$\frac{\begin{matrix}\:\:&\:\:&8&\bold{5}&6&\:\:\\\:\:&\:\:&7&\bold{9}&5&7\\\:\:&\times &\:\:&\:\:&\bold{9}&0\end{matrix}}{\begin{matrix}\:\:&\:\:&0&0&0&0\\\:\:&\:\:&6&1&3&\:\:\end{matrix}}$

Add the carried number to the multiplication $8+7\times 9=71$
$\frac{\begin{matrix}\:\:&7&\bold{8}&5&6&\:\:\\\:\:&\:\:&\bold{7}&9&5&7\\\times &\:\:&\:\:&\:\:&\bold{9}&0\end{matrix}}{\begin{matrix}\:\:&\:\:&0&0&0&0\\\:\:&1&6&1&3&\:\:\end{matrix}}$

Add the carried digit, $7$ , to the result
$\frac{\begin{matrix}\:\:&7&8&5&6&\:\:\\\:\:&\:\:&7&9&5&7\\\times &\:\:&\:\:&\:\:&9&0\end{matrix}}{\begin{matrix}\:\:&\:\:&0&0&0&0\\7&1&6&1&3&\:\:\end{matrix}}$

Add the rows to get the answer. For simplicity, fill in trailing zeros
$\frac{\begin{matrix}\:\:&\:\:&7&9&5&7\\\:\:&\times &\:\:&\:\:&9&0\end{matrix}}{\begin{matrix}0&0&0&0&0&0\\7&1&6&1&3&0\end{matrix}}$

Line up the numbers
$\begin{matrix}\:\:&\:\:&\:\:&9&0\\\times &7&9&5&7\end{matrix}$
$=716130$

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