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The sum of two numbers is …

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The sum of two numbers is 8. Determine the number if the sum of there reciprocal is 8 by 15
  • 1 answers

Sia ? 6 years, 5 months ago

Let the two numbers are x and 8 - x. 

According to question,
{tex}15\left( {\frac{1}{x} + \frac{1}{{8 - x}}} \right) = 8{/tex}
{tex} \Rightarrow 15\left( {\frac{{8 - x + x}}{{x(8 - x)}}} \right) = 8{/tex}
{tex} \Rightarrow {/tex} {tex}15 \times 8=8x(8-x){/tex}
{tex} \Rightarrow 15 = \frac{{8x}}{8}(8 - x){/tex}
{tex} \Rightarrow {/tex} 15 = x(8 - x)
{tex} \Rightarrow {/tex} 15 = 8x - x2
{tex} \Rightarrow {/tex} x2 - 8x + 15 = 0

Factorise the equation,
{tex} \Rightarrow {/tex} x2 - 5x - 3x + 15 = 0
{tex} \Rightarrow {/tex} x(x - 5) - 3(x - 5) = 0
{tex} \Rightarrow {/tex} (x - 5)(x - 3) = 0
{tex} \Rightarrow {/tex} x = 5 or x = 3
Hence, required numbers are 3 and 5.

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