Solve: 2/3 + 2/15 - 4/5 Fraction Operations with Unlike Denominators

Addition and Subtraction with Common Denominators

23+21545= \frac{2}{3}+\frac{2}{15}-\frac{4}{5}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 We want to find the least common denominator
00:06 Therefore we'll multiply by 5 and 3 respectively to find the common denominator
00:09 Remember to multiply both numerator and denominator
00:21 Let's calculate the multiplications
00:33 Subtract under the common denominator
00:38 Let's calculate the numerator
00:42 0 divided by any number is always equal to 0
00:45 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

23+21545= \frac{2}{3}+\frac{2}{15}-\frac{4}{5}=

2

Step-by-step solution

Let's try to find the lowest common denominator between 3, 15, and 5

To find the lowest common denominator, we need to find a number that is divisible by 3, 15, and 5

In this case, the common denominator is 15

Now we'll multiply each fraction by the appropriate number to reach the denominator 15

We'll multiply the first fraction by 5

We'll multiply the second fraction by 1

We'll multiply the third fraction by 3

2×53×5+2×115×14×35×3=1015+2151215 \frac{2\times5}{3\times5}+\frac{2\times1}{15\times1}-\frac{4\times3}{5\times3}=\frac{10}{15}+\frac{2}{15}-\frac{12}{15}

Now we'll add and then subtract:

10+21215=121215=015 \frac{10+2-12}{15}=\frac{12-12}{15}=\frac{0}{15}

We'll divide both the numerator and denominator by 0 and get:

015=0 \frac{0}{15}=0

3

Final Answer

0 0

Key Points to Remember

Essential concepts to master this topic
  • LCD Rule: Find the smallest number divisible by all denominators
  • Technique: Convert 23 \frac{2}{3} to 1015 \frac{10}{15} by multiplying by 55 \frac{5}{5}
  • Check: Final answer should simplify: 015=0 \frac{0}{15} = 0

Common Mistakes

Avoid these frequent errors
  • Adding denominators together instead of finding LCD
    Don't add 3 + 15 + 5 = 23 as your denominator! This creates wrong fractions that can't be combined. Always find the LCD (15) and convert each fraction to have this common denominator first.

Practice Quiz

Test your knowledge with interactive questions

Complete the following exercise:

\( \frac{1}{2}:\frac{3}{5}=\text{?} \)

FAQ

Everything you need to know about this question

How do I find the LCD of 3, 15, and 5?

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List the multiples of each number: 3: 3, 6, 9, 12, 15... 15: 15, 30, 45... 5: 5, 10, 15, 20... The smallest number that appears in all lists is 15!

Why does the second fraction stay the same?

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Since 215 \frac{2}{15} already has the LCD as its denominator, we multiply by 11 \frac{1}{1} , which doesn't change the fraction's value.

Can the answer to a fraction problem be zero?

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Yes! When the numerator equals zero (like 10 + 2 - 12 = 0), the entire fraction equals zero, regardless of the denominator.

What if I get a negative answer?

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Negative answers are completely normal! Just be careful with your addition and subtraction. In this problem: 10 + 2 - 12 = 0, but if the last term was smaller, you'd get a positive result.

Do I always need to simplify my final answer?

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Yes! Always check if your final fraction can be reduced. Since 015=0 \frac{0}{15} = 0 , we write the answer as just 0.

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