Question 789847
A man has ₱ 2,000 invested at 7% and ₱ 5,000 at 4% simple interest. What additional amount must he invest at 6% to give him an overall of 5%?
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Answer = &#8369; x 

Investments     | Rate |   Interest
------------------------------------------
  &#8369; 2,000       | .07  | &#8369; .07(2000)
  &#8369; 5,000       | .04  | &#8369; .04(5000)
  &#8369; x           | .06  | &#8369; .06(x)
------------------------------------------
&#8369;(2000+5000+x)  | .05  | &#8369; .05(2000+5000+x)

&#8369; .07(2000) + &#8369; .04(5000) + &#8369; .06(x) = &#8369; .05(2000+5000+x)
      .07(2000) + .04(5000) + .06(x) = .05(2000+5000+x)
                    140 + 200 + .06x = .05(7000+x)
                          340 + .06x = 350 + .05x
                                .01x = 10
                                   x = {{{10/.01}}}
                                   x = 1000

Answer: &#8369; 1,000

Edwin</pre>