One of the common conversions we have to carry out in science is converting from degrees centigrade to degrees Fahrenheit.
The actual formula is: °F = (°C × 9/5) + 32.
Lets try converting 30 °C to °F using this formula:
°F = (30 °C x 9/5) + 32 = (30 x 1.8) + 32 = 54 + 32 = 86
Now here is a simpler way, although it does not give the exact answer. But then we are often happy with an “order of magnitude” value, instead of an exact value. So here it is:
- Take the temperature in C, say 30 °C
- Double this temp, this gives 60 °C (so this is multiplying the original number by 2)
- Add 30. This gives 90 °F
So we can see this is fairly close to the exact value of 86.
So step 2 above (doubling ) is because in the original formula we are multiplying C by 9/5 or by 1.8. We are using the rounded value of 1.8 as 2. Then in the original formula we have to add 32, but in our approximation, we are adding only the rounded value 30.
Now this is an approximation or a “back-of-the-envelope” calculation, but its good enough for many situations like solving multiple choice questions (MCQs) in competitive exams..
Do you know of other math hacks that you would like to share here? Please reply in the comment box below and we can make a post out of it!