Say if I charged you $1000 dollars included GST (5 %). So how much is the amount before GST (5%). What is the formular to calculate this. Thank you
in Calculus Answers by

Your answer

Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
To avoid this verification in future, please log in or register.

1 Answer

If the amount before GST is x, then the amount after GST is x+x/20 because 5% is 5/100=1/20.

x+x/20=x(1+1/20)=(21/20)x. If you know the amount after tax then that means (21/20)x, so you find x be multiplying the amount by 20/21, because (20/21)(21/20)x=x.

Example: the amount after GST is $42, then the amount before tax is added is (20/21)42=$40.

by Top Rated User (897k points)

Related questions

2 answers
asked Mar 13, 2019 by anonymous | 222 views
1 answer
1 answer
asked Nov 6, 2014 in Algebra 1 Answers by anonymous | 248 views
1 answer
asked Nov 5, 2013 in Algebra 1 Answers by Vaughan | 241 views
1 answer
asked Jul 10, 2013 in Algebra 2 Answers by thatttoneguy | 260 views
1 answer
asked Dec 3, 2012 in Algebra 1 Answers by BeautifulShanaynay Level 1 User (120 points) | 303 views
Welcome to, where students, teachers and math enthusiasts can ask and answer any math question. Get help and answers to any math problem including algebra, trigonometry, geometry, calculus, trigonometry, fractions, solving expression, simplifying expressions and more. Get answers to math questions. Help is always 100% free!
86,906 questions
93,710 answers
24,246 users