Question 130551
Since the interest rate does not change and the period of investment remains unchanged, you
can do this problem by setting up a proportion: 
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interest (I) is to invested principal (P) as interest (I) is to invested principal (P)
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Which in equation form becomes:
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{{{I[1]/P[1] = I[2]/P[2]}}}
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On the left side of this equation we can substitute information from the problem. The first
amount of interest is $45 and the principal invested is $1500. Substituting these values results
in:
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{{{45/1500 = I[2]/P[2]}}}
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On the right side of the equation we know that the new principal is $2000. So we can substitute
that amount to get the equation:
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{{{45/1500 = I[2]/2000}}}
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Proportions of this form can be solved by first doing cross multiplication. Multiply the
each numerator by the denominator on the other side and set the two products equal.  
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So in this problem multiply the numerator {{{45}}} by the denominator on the other side {{{(2000)}}} 
and you get {{{(45*2000)}}}. Then multiply the numerator {{{I[2]}}} by the denominator on the other
side {{{(1500)}}} and you get {{{1500*I[2]}}}. Set the two products equal and you have the
equation:
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{{{1500*I[2]= 45*2000}}}
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Solve for {{{I[2]}}} by dividing both sides by {{{1500}}} and the equation becomes:
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{{{I[2] = (45*2000)/1500}}}
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Do the multiplication and division on the right side and you get the answer:
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{{{I[2] = 60}}}
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This tells you that at the same rate of interest and for the same period if $1500 earns $45,
then an investment of $2000 will earn $60.
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Hope this helps you to understand the problem.
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