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

 May 17th, 2018, 03:19 AM #1 Senior Member   Joined: Aug 2014 From: India Posts: 343 Thanks: 1 How to solve this crazy problem? A Certain sum amounts to 41280 in 6 years and to 29760 in 2 years at S.I. Find the sum and the rate of interest? Answer is 24000 and 12% p.a Usually they used to give one P or one T (time). But here they gave two different amounts and two different times and asking me to find one sum and one rate of interest. I am totally confused. Please help me.
 May 17th, 2018, 04:15 AM #2 Math Team   Joined: Dec 2013 From: Colombia Posts: 7,551 Thanks: 2554 Math Focus: Mainly analysis and algebra You can form two equations each having the amount and the interest rate as variables. Using those equations, you can eliminate one variable and thus solve for the other. Substitute and solve for the remaining variable.
 May 17th, 2018, 05:47 AM #3 Math Team   Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,785 Thanks: 970 a = start sum, r = rate Code: YEAR BALANCE 0 a 2 29760 = a + 2*a*r [Eq 1] 6 41280 = a + 6*a*r [Eq 2] Those are the 2 equations Archibald means... Thanks from Ganesh Ujwal
 May 17th, 2018, 10:34 AM #4 Senior Member   Joined: Aug 2014 From: India Posts: 343 Thanks: 1 Now should I have to eliminate R and find P?
 May 17th, 2018, 10:42 AM #5 Math Team   Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,785 Thanks: 970 Yes, and EASY to do: 2 equations and 2 variables. Get to work! Thanks from Ganesh Ujwal
May 17th, 2018, 10:51 AM   #6
Senior Member

Joined: May 2008

Posts: 298
Thanks: 81

Beer soaked ramblings follow.
Quote:
 Originally Posted by v8archie You can form two equations each having the amount and the interest rate as variables. Using those equations, you can eliminate one variable and thus solve for the other. Substitute and solve for the remaining variable.
Has thou forgotten thy promise to put Ganesh on thy ignore list?
Quote:
 Originally Posted by Denis a = start sum, r = rate Code: YEAR BALANCE 0 a 2 29760 = a + 2*a*r [Eq 1] 6 41280 = a + 6*a*r [Eq 2] Those are the 2 equations Archibald means...
Ah Sir D, didst thou also forgot Ganesh' command for you to give a complete worked out solution instead of half baked cryptic clues that will force Ganesh to actually do some real work?

 May 17th, 2018, 10:01 PM #7 Senior Member   Joined: Aug 2014 From: India Posts: 343 Thanks: 1 I got the answer.
 May 18th, 2018, 05:12 AM #8 Math Team   Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,785 Thanks: 970 Congratulations! Why don't you show your steps to solving, as it may help a student: this is main purpose of this site...
May 18th, 2018, 05:33 AM   #9
Math Team

Joined: Dec 2013
From: Colombia

Posts: 7,551
Thanks: 2554

Math Focus: Mainly analysis and algebra
Quote:
 Originally Posted by jonah Has thou forgotten thy promise to put Ganesh on thy ignore list?
I never made such a promise. But I'm not dishing out answers, only hints.

 May 18th, 2018, 06:37 AM #10 Global Moderator   Joined: Dec 2006 Posts: 20,095 Thanks: 1905 By subtraction, 11520 = 4ar, so 5760 = 2ar. Hence a = 29760 - 5760 = 24000, and so r = 5760/48000 = 0.12 = 12%. There are various other ways of solving the two equations.

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