💡 What You Will Learn
The GED gives you the formula C = (5/9)(F − 32) and asks you to use it backwards — given a Celsius temperature, find the Fahrenheit value. This means solving an equation for F. This lesson teaches both directions and how to solve the GED problem step by step!
32 — the freezing point offset
9/5 = 1.8 — the scale ratio
5/9 ≈ 0.556 — the inverse ratio
The GED gives C = (5/9)(F − 32) and asks for F. You must solve for F — plug in C and use inverse operations!
| Temperature | °Celsius | °Fahrenheit |
|---|---|---|
| Water freezes | 0°C | 32°F |
| Water boils | 100°C | 212°F |
| Body temp | 37°C | 98.6°F |
| Scales equal | −40°C | −40°F |
1. Multiply the Celsius temperature by 9/5 (or 1.8)
2. Add 32 to the result
3. The answer is the Fahrenheit temperature
F = (9/5) × 25 + 32
F = 45 + 32
(9/5) × C = multiply C by 9, then divide by 5.
Example: (9/5) × 25 = 225 ÷ 5 = 45 ✅
1. Subtract 32 from the Fahrenheit temperature
2. Multiply the result by 5/9
3. The answer is the Celsius temperature
C = (5/9)(77 − 32)
C = (5/9)(45)
C = 25
Always subtract 32 BEFORE multiplying by 5/9. If you multiply first and subtract later you'll get the wrong answer. Parentheses in (F − 32) tell you to do subtraction first!
The formula gives us C in terms of F. We're given C = −25 and need to find F. This means we set the formula equal to −25 and solve for F using inverse operations — it's a two-step equation!
−25 = (5/9)(F − 32)
−25 × (9/5) = F − 32
(−25 × 9) ÷ 5 = F − 32
−225 ÷ 5 = F − 32
−45 = F − 32
−45 + 32 = F
−13 = F
| Choice | How You'd Get It | Correct? |
|---|---|---|
| −13°F | −25 × (9/5) + 32 = −45 + 32 = −13 ✅ | ✅ CORRECT |
| 13°F | Forgot the negative sign on −25 ❌ | ❌ Wrong |
| −32°F | Just added 32 without multiplying by 9/5 ❌ | ❌ Wrong |
| 18°F | Used wrong fraction or wrong sign somewhere ❌ | ❌ Wrong |
°C → °F: Try −25 → should get −13 | Try 100 → should get 212 | Try 0 → should get 32
°F → °C: Try 32 → should get 0 | Try 212 → should get 100 | Try 98.6 → should get 37
| °Celsius | °Fahrenheit | Context |
|---|---|---|
| −40°C | −40°F | The only point where both scales are equal |
| −25°C | −13°F | The GED problem answer ⭐ |
| 0°C | 32°F | Water freezes |
| 20°C | 68°F | Comfortable room temperature |
| 37°C | 98.6°F | Normal human body temperature |
| 100°C | 212°F | Water boils |
🔑 Memory Tips
30°C ≈ 86°F — A hot summer day
0°C = 32°F — "Zero = Thirty-Two" (freezing)
−40° = −40° — Both scales meet at negative forty!