POPStudying

Cambridge 0580 IGCSE  ·  Topic C1.5

C1.5 Ordering

Image  ·  914 × 270

01 — Explanation

What do the inequality symbols mean?

SymbolMeaning
==Equal to
≠\neqNot equal to
<<Strictly less than
>>Strictly greater than
⩽\leqslantLess than or equal to
⩾\geqslantGreater than or equal to

The symbol always points its narrow end towards the smaller value, like an arrow: 3<73 < 7.

02 — Explanation

How do I compare values given in different forms?

Convert both sides to the same format — usually decimals — before comparing.

Example: insert <<, >> or == between 0.64\sqrt{0.64} and 80%80\%.

Evaluate both: 0.64=0.8\sqrt{0.64} = 0.8 and 80%=0.880\% = 0.8. They match exactly, so 0.64=80%\sqrt{0.64} = 80\%.

Rounding Warning

if two values are close together (e.g. 0.16=0.4\sqrt{0.16} = 0.4 versus 45%=0.4545\% = 0.45), don't round too early — keep 3–4 decimal places while comparing, or you may create a false tie.

03 — Explanation

How do negative numbers change the ordering?

This is the part that catches people out: for negative numbers, the one with the larger magnitude (the "bigger-looking" number) is actually smaller.

−9<−4-9 < -4

Think of a number line: −9-9 sits further to the left than −4-4, so it represents a smaller value — even though 9>49 > 4 as positive numbers.

04 — Explanation

How do I write a description in words as an inequality?

Exam questions sometimes describe a range in words and ask you to write it using symbols. Translate one phrase at a time, and check whether each end of the range is included:

  • "at least 55" → x⩾5x \geqslant 5 (5 itself is allowed)
  • "more than 55" → x>5x > 5 (5 itself is not allowed)
  • "at least 55 but less than 1212" → 5⩽x<125 \leqslant x < 12

Example: a lift is only safe carrying a load of at least 00 kg and strictly less than 630630 kg. Write this as an inequality for the load, LL.

0⩽L<6300 \leqslant L < 630

The lower end uses ⩽\leqslant because a load of exactly 00 kg is fine, but the upper end uses << because 630630 kg itself is not safe.

Common Slip

using ⩽\leqslant on both ends by default. Always check the wording carefully — "at least" and "at most" include the boundary value, while "more than" and "less than" strictly exclude it.

05 — Worked example

Worked exam-style question

Order the following from smallest to largest: −12,0.4,−0.55,0.16,45%-\dfrac{1}{2}, \quad 0.4, \quad -0.55, \quad \sqrt{0.16}, \quad 45\%.

  1. Convert each to a decimal: −12=−0.5-\frac{1}{2} = -0.5, 0.4=0.40.4 = 0.4, −0.55=−0.55-0.55 = -0.55, 0.16=0.4\sqrt{0.16} = 0.4, 45%=0.4545\% = 0.45.
  2. Order the decimals, remembering negatives with a larger magnitude come first:
−0.55<−0.5<0.4=0.4<0.45-0.55 < -0.5 < 0.4 = 0.4 < 0.45
  1. Restate using the original forms:
−0.55,−12,0.4,0.16,45%-0.55, \quad -\frac{1}{2}, \quad 0.4, \quad \sqrt{0.16}, \quad 45\%

06 — Common mistakes

Common mistakes to avoid

  • Assuming negative numbers order the same way as positives — since 9>49 > 4, wrongly concluding −9>−4-9 > -4. It's the reverse: −9<−4-9 < -4.
  • Confusing "ascending" and "descending" under time pressure. Ascending = smallest to largest (climbing up); descending = largest to smallest.
  • Rounding too early when two converted values are close, which can create a tie that isn't really there.