Exercises: multiplying decimal numbers

Multiplying decimal fractions

$2.5\cdot 10$

Since you are multiplying a decimal fraction with $10$, you can simply shift the decimal mark by one place to the right.

$=25$

Multiplying decimal fractions

$2.5\cdot 0.1$

Since you are multiplying the decimal fraction with $0.1$ you can simply shift the decimal mark by one place to the left.

$=0.25$

Multiplying decimal fractions

$5.1\cdot 2.9$

Ignore the decimal marks and multiply the two figures.

$\begin{array}{l}\underline{\phantom{0.}51\cdot 29}\\ \phantom{\mathrm{5,10}}459\\ \underline{\phantom{\mathrm{5,1}}1020}\\ \phantom{500}1479\end{array}$

Place the decimal mark in the result in a way so that the solution contains as many decimal places as both coefficients combined, in this case $1+1=2$ places.

$\to 14.79$

Multiplying decimal fractions

$2.45\cdot 0.671$

Ignore the decimal marks and multiply the two figures.

$\begin{array}{l}\underline{\phantom{,0,}245\cdot 671}\\ \phantom{\mathrm{2,45000}}245\\ \phantom{\mathrm{2,450}}17150\\ \underline{\phantom{\mathrm{2,45}}147000}\\ \phantom{\mathrm{24,5}}164395\end{array}$

Place the decimal mark in the result in a way so that the solution contains as many decimal places as both coefficients combined, in this case $2+3=5$ places.

$\to 1.64395$

Multiplying decimal fractions

$9\cdot 0.686$

Ignore the decimal marks and multiply the two figures.

$\begin{array}{l}\underline{\phantom{0,}9\cdot 686}\\ \phantom{90000}54\\ \phantom{9000}720\\ \underline{\phantom{900}5400}\\ \phantom{\mathrm{9,0}}6174\end{array}$

Place the decimal mark in the result in a way so that the solution contains as many decimal places as both coefficients combined, in this case $0+3=3$ places.

$\to 6.174$

Multiplying decimal fractions

$2.5\cdot 100$

Since you are multiplying the decimal fraction with $100$ you can simply shift the decimal mark two places to the right.

$=250$