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Pearson Edexcel 4MA1 IGCSE  ·  Topic G3.2

G3.2 Fractions: Equivalence, Conversion & the Four Operations

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01 — Explanation

What does a fraction actually represent?

A fraction is a single value, not two separate whole numbers. In 34\dfrac{3}{4}, the denominator (44) tells you the size of the pieces (quarters), and the numerator (33) tells you how many of those pieces you have. The denominator never changes just because you're adding or subtracting — it's a unit label, like "cm" or "kg", not a number to be operated on separately.

02 — Explanation

What's the difference between proper, improper, and mixed fractions?

  • Proper fraction: numerator smaller than denominator, value <1<1 (e.g. 34\frac{3}{4}).
  • Improper fraction: numerator ≥\ge denominator, value ≥1\ge 1 (e.g. 114\frac{11}{4}).
  • Mixed number: a whole number plus a proper fraction (e.g. 2342\frac{3}{4}).

To convert mixed → improper: multiply the whole number by the denominator, add the numerator, keep the same denominator. 234=(2×4)+34=1142\frac{3}{4} = \dfrac{(2\times4)+3}{4} = \dfrac{11}{4}.

To convert improper → mixed: divide numerator by denominator; the quotient is the whole number, the remainder sits over the original denominator. 114=11÷4=2\dfrac{11}{4} = 11 \div 4 = 2 remainder 33, so 2342\frac{3}{4}.

Exam Tip: Before adding or subtracting mixed numbers, always convert to improper fractions first. Trying to combine whole-number and fraction parts separately is the single most common place marks are lost on this topic.

03 — Explanation

How do I find equivalent fractions and simplify?

Equivalent fractions represent the same value — multiply (or divide) numerator and denominator by the same non-zero number, since that's equivalent to multiplying by 11 (e.g. 33=1\frac{3}{3}=1). 48=12\dfrac{4}{8}=\dfrac{1}{2}.

To simplify, divide numerator and denominator by their highest common factor (HCF) until no common factor remains. This isn't optional — "simplest form" is often an explicit mark on the paper.

04 — Explanation

How do I add or subtract fractions?

They must share a denominator first. If denominators differ, find the LCM of the denominators and convert both fractions to it, then add or subtract just the numerators — the denominator stays fixed.

23+16=46+16=56\frac{2}{3}+\frac{1}{6} = \frac{4}{6}+\frac{1}{6} = \frac{5}{6}

Common Misconception: Adding both numerators and denominators (e.g. 24+54\frac{2}{4}+\frac{5}{4} "becomes" 78\frac{7}{8}). Since the denominator is a fixed unit size, it can never change during addition — only the count of pieces (the numerator) does.

05 — Explanation

How do I multiply and divide fractions?

Multiply: multiply the numerators together, and the denominators together. 45×23=815\dfrac{4}{5}\times\dfrac{2}{3}=\dfrac{8}{15}.

Divide: keep the first fraction, change ÷ to ×, flip the second fraction (its reciprocal). 27÷34=27×43=821\dfrac{2}{7}\div\dfrac{3}{4}=\dfrac{2}{7}\times\dfrac{4}{3}=\dfrac{8}{21}.

A quick sanity check for "invert and multiply": dividing 88 by 22 gives the same answer as multiplying 88 by 12\frac{1}{2} — dividing by a number is always the same as multiplying by its reciprocal.

06 — Explanation

How do I order fractions with different denominators?

  1. Find the LCM of all the denominators (the lowest common denominator).
  2. Convert every fraction to that denominator.
  3. Order by comparing the numerators only.

To order 25,13,715\frac{2}{5}, \frac{1}{3}, \frac{7}{15}: LCD is 1515, giving 615,515,715\frac{6}{15}, \frac{5}{15}, \frac{7}{15} — so the order is 13<25<715\frac{1}{3} < \frac{2}{5} < \frac{7}{15}.

Common Misconception: Assuming a bigger denominator always means a bigger fraction (true only when numerators match). 18<14\frac{1}{8} < \frac{1}{4} because eighths are smaller pieces than quarters — more pieces to make a whole means each piece is smaller.

07 — Worked example

Worked Example

Calculate 523−2345\frac{2}{3} - 2\frac{3}{4}, giving your answer as a mixed number in its simplest form.

  1. Convert to improper fractions: 523=1735\frac{2}{3}=\frac{17}{3}, 234=1142\frac{3}{4}=\frac{11}{4}.
  2. Common denominator of 33 and 44 is 1212: 173=6812\frac{17}{3}=\frac{68}{12}, 114=3312\frac{11}{4}=\frac{33}{12}.
  3. Subtract: 6812−3312=3512\frac{68}{12}-\frac{33}{12}=\frac{35}{12}.
  4. Convert back to a mixed number: 35÷12=235 \div 12 = 2 remainder 1111, so 211122\frac{11}{12}.