Maybe its the way you say it thats confusing to your work colleagues? Because £100 take away 20% is £80. If you mean the total plus VAT is £100 and what is the value of the VAT if VAT is 20%? Then thats a totally different answer.What I find odd is spelling gets jumped all over on forums and at work but a basic lack of maths skills is seen as acceptable - I've seen people add two amounts under £100 get an answer over £1,000 out of their calculator at work (due to input error) and put that amount in a letter to a customer without batting an eyelid at the answer they got and people that have worked in an office for years thinking £100 take away 20% VAT is £80. To me that's much worse than spelling errors.