SOLUTION: In April, Bob changed 1140 Indian Rupees into German Marks when the rate of exchange was x Rupees = 1 Mark. In August, he again changed 1140 Rupees into Marks. The rate of exchange

Algebra ->  Expressions -> SOLUTION: In April, Bob changed 1140 Indian Rupees into German Marks when the rate of exchange was x Rupees = 1 Mark. In August, he again changed 1140 Rupees into Marks. The rate of exchange      Log On


   

Question 1018734: In April, Bob changed 1140 Indian Rupees into German Marks when the rate of exchange was x Rupees = 1 Mark. In August, he again changed 1140 Rupees into Marks. The rate of exchange was then (x+1) Rupees = 1 Mark. He received 3 Marks less in April than he did in August. Solve the equation: x^2 + x - 380 = 0 to find the rate of exchange in April.
How? I understand the equation and everything else, but I am just stuck on the last bit of the question. How do you do this?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
In April, Bob will receive Marks according to:
+1140%2A%28+1%2Fx+%29+
In August, he received Marks according to:
+1140%2A%28+1%2F%28x%2B1%29%29+
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He received 3 Marks less in April than he did in August.
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+1140%2A%28+1%2Fx+%29+=+1140%2A%28+1%2F%28x%2B1%29%29+-+3+
Multiply both sides by +x%2A%28+x%2B1+%29+
+1140%2A%28+x%2B1+%29+=+1140x+-+3%2Ax%2A%28+x%2B1+%29+
+1140x+%2B+1140+=+1140x+-+3x%5E2+-+3x+
+1140+=+-3x%5E2+-+3x+
+x%5E2+%2B+x+%2B+380+=+0+
I get a different equation ( sign of 380 )
I'll use the one they gave:
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Use quadratic formula
+x+=+%28-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
+a+=+1+
+b+=+1+
+c+=+-380+
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+x+=+%28-1+%2B-+sqrt%28+1%5E2+-+4%2A1%2A%28-380%29+%29%29+%2F+%282%2A1%29+
+x+=+%28-1+%2B-+sqrt%28+1+-+4%2A1%2A%28-380%29%29%29+%2F+%282%2A1%29+
+x+=+%28+-1+%2B+sqrt%28+1521+%29%29+%2F+2+
+x+=+%28+-1+%2B+39+%29+%2F+2+
+x+=+38%2F2+
+x+=+19+
The rate in April was 19 Rupees = 1 Mark
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I looked over my algebra, and I don't see why I
got a different equation. Their's work and mine doesn't
Can you see my mistake?