Any tips on how to calculate

mental math
Recent activity on Sep 18, 2018
4 Answers
2.0 k Views
Dario asked on Sep 17, 2018

I have problems getting a decent score in the hard section of the "percent" exercises in the Mental Math tool here on the site.

Any tips on how to solve this kind of complex operations?

(edited)

Overview of answers

Upvotes
  • Upvotes
  • Date ascending
  • Date descending
Best answer
Anonymous replied on Sep 18, 2018

Another little tip is to practice with multiplications, rather than divisions. It seems to be easier on the brain.

E.g. 30% of 7 is easier done this way:

1) 7 x 30 = 210

2) Divide by 100.

Was this answer helpful?
2
Anonymous replied on Sep 18, 2018

All good tips below. Ultimately it comes down to personal preference. My tips for dealing with percentages (especially complex ones): think of everything in terms of divisions of 10 and 2 --> i.e. almost any percentage, you can reach by dividing your initial number by 10 or by 2

Example - 37.5% of 460:

- 30% =3*10% = 46*3= 138

- 5% = 23

- 2.5% = 11.5

37.5% = 138+23+11.5 =172.5

Hope this helps!

Alessandro

Was this answer helpful?
1
Vlad
Expert
Content Creator
replied on Sep 17, 2018
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School

Hi,

Simply learn the division table up to 1/11 (i.e. 5/6 = 83.3%). It will help you calculate any percentage problems

Best

Was this answer helpful?
Anonymous replied on Sep 17, 2018

Practice, practice, practice...

Also, there are some shortcuts I find useful:

  • 90% of X - just divide X by 10 and subtract from X.
  • x% of 1xx - maybe easier to take (x% * 100) + (x% * xx)
  • 20 / 40 / 60 / 80% of 65 / 75 / 85: Take 20 / 40 ... % of 70 / 80 / 90 and subtract 1 / 2 / 3 / 4. So 40% of 65 = 40% of 70 - 2 = 28 - 2 = 26
Was this answer helpful?
1