Question 1018734
In April, Bob will receive Marks according to:
{{{ 1140*( 1/x ) }}}
In August, he received Marks according to:
{{{ 1140*( 1/(x+1)) }}}
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He received 3 Marks less in April than he did in August.
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{{{ 1140*( 1/x ) = 1140*( 1/(x+1)) - 3 }}}
Multiply both sides by {{{ x*( x+1 ) }}}
{{{ 1140*( x+1 ) = 1140x - 3*x*( x+1 ) }}}
{{{ 1140x + 1140 = 1140x - 3x^2 - 3x }}}
{{{ 1140 = -3x^2 - 3x }}}
{{{ x^2 + x + 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 = (-b +- sqrt( b^2 - 4*a*c )) / (2*a) }}}  
{{{ a = 1 }}}
{{{ b = 1 }}}
{{{ c = -380 }}}
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{{{ x = (-1 +- sqrt( 1^2 - 4*1*(-380) )) / (2*1) }}}  
{{{ x = (-1 +- sqrt( 1 - 4*1*(-380))) / (2*1) }}}  
{{{ x = ( -1 + sqrt( 1521 )) / 2 }}}
{{{ x = ( -1 + 39 ) / 2 }}}
{{{ x = 38/2 }}}
{{{ 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?