Mental Math - Calculating Percents (Fraction to Decimal)

Hi there!

The two main techniques are either 

Rouding: 21/87 = 20/45 = 4/9 = ~4

OR 

Simplification: 21/87 (they can all be simplied by 3) = 7/29 = ~4

Even so, long division is your friend. If you get comfortable with it you can be quite fast. 

Also, last but not least, speed does't matter as much as clarity of communication and depth of interpretation (of the result). So don't worry so much about how fast your are. It's not a speed contest. It's a conversation.

Best,
Cristian

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Hi there,

I would be happy to share my thoughts on your question:

• First of all, using common factors to simplify numbers may help a lot. For instance, if you see numbers like 21 and 87, knowing they are both divisible by 3 can reduce it to 7/29, making it easier to handle.
• Moreover, approximations are your best friend in these situations. If you round numbers to the nearest 5 or 10, it becomes much easier. Like 113 can be approximated to 110, and 455 can be rounded to 450, making the calculation 110/450 which is roughly 1/4 or 25%.
• Lastly, it is absolutely fine to take your time to run complex multiplications and divisions manually.

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Best,

Hagen

Hi there,

Personally, I love rocketblocks and math-drills for this.

For your examples there are two main aspects (and it depends):

1. Learn long division. You're going to need ot
2. Implement rounding and shortcuts (like my doubling-halving technique or my splitting technique)

Hi there,

Q: I was hoping to get some tips or resources on how to convert fractions into decimals to calculate percents. 

I would start by asking if you can approximate. Taking as an example 21/87:

1. If you can :
   1. Simplify as 20/90= 2/9 = 22%
   2. Since the denominator is lower and the numerator higher, explain the real final number should be a bit higher
2. If you cannot, you will have to do the actual division:
   1. Recognize that 21/87= 0.2 with a remainder
   2. Remainder: 21-17.4=3.6 (17.4 comes from 87*0.2, or 8.7*2)
   3. Recognize that 36/87= 4 with a remainder
   4. Result is 0.24 with a remainder
   5. Most of the time this will be enough, if not, you can continue

Best,

Francesco

Hi,

Rounding is your friend here, like others have mentioned.

My POV on this is if you have really strong comfort with the core functions (addition, subtraction, division, multiplication) → then percentages and fractions are just a subset of that.