Comparing fractions determines which of two values is larger, smaller, or whether they are equal. Several methods exist, each suited to different situations. Simple cases with matching numerators or denominators resolve by inspection, while more complex comparisons require finding common denominators, cross-multiplying, or converting to decimals.
Comparing Fractions with Same Denominator
When two fractions share a denominator, compare their numerators directly. The fraction with the larger numerator is the larger fraction.
85>83
Both fractions represent eighths. Five eighths is more than three eighths because five pieces exceed three pieces of the same size.
This principle extends to any number of fractions with a common denominator. Arranging 92, 97, and 94 in order requires only sorting the numerators: 92<94<97.
Comparing Fractions with Same Numerator
When two fractions share a numerator, compare their denominators inversely. The fraction with the smaller denominator is the larger fraction.
43>73
Both fractions take three parts, but fourths are larger pieces than sevenths. Three large pieces exceed three small pieces.
This inverse relationship often surprises at first. The key insight is that larger denominators create smaller individual pieces. Dividing something into 100 parts produces much smaller pieces than dividing it into 2 parts.
Common Denominator Method
When neither numerator nor denominator matches, convert both fractions to equivalent fractions with a common denominator, then compare numerators.
To compare 43 and 65, find a common denominator. The LCM of 4 and 6 is 12.
43=129and65=1210
Since 10>9, we have 65>43.
This method always works and is the most reliable approach when other shortcuts do not apply.
Cross-Multiplication Method
Cross-multiplication provides a shortcut that avoids explicitly finding a common denominator. To compare ba and dc, compute the cross products a×d and b×c. The larger cross product indicates the larger fraction.
To compare 73 and 94:
3×9=27and7×4=28
Since 28>27, we have 94>73.
The rule: multiply each numerator by the opposite denominator. The cross product stays on the same side as its numerator. If a×d>b×c, then ba>dc.
Benchmark Fractions
Benchmark fractions like 0, 21, and 1 provide quick reference points for estimation and comparison without calculation.
To compare 83 and 95: note that 83<21 (since 3<4) while 95>21 (since 5>4.5). Therefore 95>83 without any cross-multiplication.
Other useful benchmarks include 41 and 43. With practice, recognizing whether a fraction is close to 0, near 21, or approaching 1 speeds up many comparisons.
Decimal Conversion Method
Converting fractions to decimals allows direct numerical comparison. Divide the numerator by the denominator for each fraction.
To compare 85 and 117:
85=0.625and117≈0.636
Since 0.636>0.625, we have 117>85.
This method is practical with a calculator or for fractions that produce simple decimals. It becomes cumbersome for fractions with long repeating decimals.
Comparing Mixed Numbers
Compare mixed numbers by first examining the whole parts. The mixed number with the larger whole part is larger overall.
581>487
Five wholes exceed four wholes regardless of the fractional parts.
When whole parts are equal, compare the fractional parts using any method from this page. For 352 versus 373, cross-multiply the fractions: 2×7=14 and 5×3=15. Since 15>14, we have 73>52, so 373>352.
Ordering Multiple Fractions
To arrange several fractions in order, find a common denominator for all of them and compare the resulting numerators.
Order 32, 43, 65, and 127 from least to greatest. The LCD of 3, 4, 6, and 12 is 12.
32=128,43=129,65=1210,127=127
Sorting by numerators: 7<8<9<10. The order is 127<32<43<65.
Number Line Visualization
Placing fractions on a number line shows their relative positions visually. Fractions further to the right are larger.
The interval from 0 to 1 can be subdivided according to any denominator. Marking fourths at 41, 42, 43 and thirds at 31, 32 shows that 31 lies between 41 and 42, confirming 41<31<21.
Number lines are particularly useful for developing intuition about fraction size and for understanding why certain comparison methods work. Seeing that 32 and 64 occupy the same point reinforces the concept of equivalent fractions.