My Math Forum percentage % of a number

 Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion

 March 24th, 2009, 03:10 AM #1 Newbie   Joined: Mar 2009 Posts: 1 Thanks: 0 percentage % of a number okay i'm currently studying for a ASVAB test for the military. and they have questions like the one below, " what number is 5% of 2000 " how would i solve for something like that? or they have " 35% of what number is 70 " " if 45 is 120% of a number, what is 80% of the same number? " " if 6 is 24% of a number, what is 40% of the same number? " " 25% of \$900= " questions like those, please help!
 March 24th, 2009, 06:15 AM #2 Global Moderator   Joined: Dec 2006 Posts: 18,053 Thanks: 1395 The symbol "%" means "hundredths", so 120% means 120/100 or 1.2, and 5% is 5/100 or 1/20 or 0.05. Hence, in particular, "50%" means "half", "100% of" means "all", "200% of" means "twice", etc. For problems such as "What number is 5% of 2000?" (or "Find 5% of 2000."), just multiply 0.05 by 2000 to get the answer. The problem "35% of what number is 70?" corresponds to the equation: (35/100) * x = 70, where x is the number to be found. Dividing both sides of this equation by 0.35 gives x = 70/0.35. Does this help you enough for you to complete these problems and do the remaining problems?
 March 25th, 2009, 04:15 PM #3 Senior Member   Joined: Jul 2008 Posts: 895 Thanks: 0 Re: percentage % of a number Write it literally [word for word]. The = sign is the verb in the sentence, and "of" means "times", or "multiply", as in three quarters of 12 is 9 ... 3/4x12 = 9. " what number is 5% of 2000 " N = 5/100x2000 = 100 " 35% of what number is 70 " 35/100xN = 70 Solve for N ...You must be able to do some algebra from past experience. If not, start again. " if 45 is 120% of a number, what is 80% of the same number? " 45 = 120/100xN Solve for N, then find 80% of N. etc...
March 26th, 2009, 02:48 AM   #4
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Quote:
 Originally Posted by lambofgod if 6 is 24% of a number, what is 40% of the same number?
40% is 40/24 of 24%, i.e., 5/3 of 24%, so the answer is 5/3 of 6, i.e., 10.

March 26th, 2009, 04:31 AM   #5
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Re:

Quote:
Originally Posted by skipjack
Quote:
 Originally Posted by lambofgod if 6 is 24% of a number, what is 40% of the same number?
40% is 40/24 of 24%, i.e., 5/3 of 24%, so the answer is 5/3 of 6, i.e., 10.
Why not, as I suggested earlier, a literal translation?

6 is 24% of a number

6 = 24/100xN
N = 6x100/24 = 25

what is 40% of the same number?

N1 = 40/100xN = 40/100x25 = 10

 March 28th, 2009, 03:52 AM #6 Global Moderator   Joined: Dec 2006 Posts: 18,053 Thanks: 1395 No reason why not. I was giving a process suited to mental arithmetic (as I understand it, the ASVAB is a multiple choice test).
March 28th, 2009, 04:12 AM   #7
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Re:

Quote:
 Originally Posted by skipjack No reason why not. I was giving a process suited to mental arithmetic (as I understand it, the ASVAB is a multiple choice test).
I hadn't realised that. Of course, one's approach is different for such tests, even as in some math competitions. However, I have always had a passionate dislike of multiple choice, based on personal experiences, and consider that is how some people get their driver's license.

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