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May 17th, 2018, 02:19 AM   #1
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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.
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May 17th, 2018, 03:15 AM   #2
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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.
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May 17th, 2018, 04:47 AM   #3
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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...
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May 17th, 2018, 09:34 AM   #4
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Now should I have to eliminate R and find P?
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May 17th, 2018, 09:42 AM   #5
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Yes, and EASY to do: 2 equations and 2 variables.

Get to work!
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May 17th, 2018, 09:51 AM   #6
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Beer soaked ramblings follow.
Quote:
Originally Posted by v8archie View Post
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 View Post
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?
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May 17th, 2018, 09:01 PM   #7
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I got the answer.
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May 18th, 2018, 04:12 AM   #8
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Congratulations!
Why don't you show your steps to solving,
as it may help a student: this is main purpose of this site...
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May 18th, 2018, 04:33 AM   #9
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Quote:
Originally Posted by jonah View Post
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.
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May 18th, 2018, 05:37 AM   #10
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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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