how to multiply fractions with whole numbers
To multiply fractions with whole numbers, turn the whole number into a fraction, multiply straight across (top with top, bottom with bottom), then simplify if you can.
Whatβs going on when you multiply?
Think of multiplying a fraction by a whole number as repeated addition.
For example, 14Γ3\frac{1}{4}\times 341βΓ3 means βthree groups of one-quarter,β the same as 14+14+14\frac{1}{4}+\frac{1}{4}+\frac{1}{4}41β+41β+41β.
Stepβbyβstep method
Use these steps every time:
- Write the whole number as a fraction.
- Example: 5 becomes 51\frac{5}{1}15β.
- Multiply the numerators (top numbers).
- Example: 23Γ4=23Γ41β2Γ4=8\frac{2}{3}\times 4=\frac{2}{3}\times \frac{4}{1}\Rightarrow 2\times 4=832βΓ4=32βΓ14ββ2Γ4=8.
- Multiply the denominators (bottom numbers).
- Continuing: 3Γ1=33\times 1=33Γ1=3, so you get 83\frac{8}{3}38β.
- Simplify or turn into a mixed number if needed.
- 83=223\frac{8}{3}=2\frac{2}{3}38β=232β because 8 Γ· 3 = 2 remainder 2.
A few quick examples
Think of each one as βthat fraction, this many times in a row.β
- 18Γ5\frac{1}{8}\times 581βΓ5
- Turn 5 into a fraction: 51\frac{5}{1}15β.
- Multiply: 18Γ51=1Γ58Γ1=58\frac{1}{8}\times \frac{5}{1}=\frac{1\times 5}{8\times 1}=\frac{5}{8}81βΓ15β=8Γ11Γ5β=85β.
- 34Γ4\frac{3}{4}\times 443βΓ4
- 4=414=\frac{4}{1}4=14β.
- 34Γ41=3Γ44Γ1=124=3\frac{3}{4}\times \frac{4}{1}=\frac{3\times 4}{4\times 1}=\frac{12}{4}=343βΓ14β=4Γ13Γ4β=412β=3.
- 13Γ15\frac{1}{3}\times 1531βΓ15
- 15=15115=\frac{15}{1}15=115β.
- 1Γ153Γ1=153=5\frac{1\times 15}{3\times 1}=\frac{15}{3}=53Γ11Γ15β=315β=5.
What about mixed numbers?
If you have a mixed number (like 1251\frac{2}{5}152β) and a whole number, thereβs just one extra step.
- Turn the mixed number into an improper fraction.
- 125=751\frac{2}{5}=\frac{7}{5}152β=57β (because 1Γ5+2=71\times 5+2=71Γ5+2=7).
- Turn the whole number into a fraction.
- 10 becomes 101\frac{10}{1}110β.
- Multiply numerators and denominators.
- 75Γ101=7Γ105Γ1=705\frac{7}{5}\times \frac{10}{1}=\frac{7\times 10}{5\times 1}=\frac{70}{5}57βΓ110β=5Γ17Γ10β=570β.
- Simplify.
- 705=14\frac{70}{5}=14570β=14.
Handy mental shortcut
Sometimes you can simplify early:
- Example: 45Γ25\frac{4}{5}\times 2554βΓ25
- Write as fractions: 45Γ251\frac{4}{5}\times \frac{25}{1}54βΓ125β.
- Notice 25 Γ· 5 = 5, so cancel: 45Γ251=4Γ5=20\frac{4}{\cancel{5}}\times \frac{\cancel{25}}{1}=4\times 5=205β4βΓ125β=4Γ5=20.
This βsimplify before multiplyingβ trick keeps numbers smaller and easier to work with.
Mini practice (with answers)
Try these in your head or on paper:
- 25Γ3=?\frac{2}{5}\times 3=?52βΓ3=?
- 56Γ4=?\frac{5}{6}\times 4=?65βΓ4=?
- 213Γ3=?2\frac{1}{3}\times 3=?231βΓ3=?
Answers:
- 25Γ3=65=115\frac{2}{5}\times 3=\frac{6}{5}=1\frac{1}{5}52βΓ3=56β=151β.
- 56Γ4=206=103=313\frac{5}{6}\times 4=\frac{20}{6}=\frac{10}{3}=3\frac{1}{3}65βΓ4=620β=310β=331β.
- 213=732\frac{1}{3}=\frac{7}{3}231β=37β, so 73Γ3=213=7\frac{7}{3}\times 3=\frac{21}{3}=737βΓ3=321β=7.
Simple HTML table of examples
Since you asked for tables as HTML, hereβs a quick reference:
html
<table>
<tr>
<th>Expression</th>
<th>Step as Fractions</th>
<th>Product</th>
<th>Mixed Number</th>
</tr>
<tr>
<td>1/8 Γ 5</td>
<td>(1/8) Γ (5/1)</td>
<td>5/8</td>
<td>5/8</td>
</tr>
<tr>
<td>3/4 Γ 4</td>
<td>(3/4) Γ (4/1)</td>
<td>12/4</td>
<td>3</td>
</tr>
<tr>
<td>1/3 Γ 15</td>
<td>(1/3) Γ (15/1)</td>
<td>15/3</td>
<td>5</td>
</tr>
<tr>
<td>1 2/5 Γ 10</td>
<td>(7/5) Γ (10/1)</td>
<td>70/5</td>
<td>14</td>
</tr>
</table>
TL;DR:
- Turn the whole number into a fraction with 1 on the bottom.
- Multiply tops, multiply bottoms, then simplify or turn into a mixed number.
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