Question 95730
Let N equal the number of nickels.
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Since the number of dimes is to be twice the number of nickels, the number of dimes is 2*N.
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And since the number of quarters is to be three times the number of nickels, the number of
quarters is 3*N
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Since there are N nickels and each nickel is $0.05, the amount of money from nickels will
be 0.05*N.
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Since there are 2*N dimes and each dime is $0.10, the amount of money from dimes will be
(0.10)*2*N which equals 0.2*N.
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Finally since there are 3*N quarters and each quarter is $0.25, the amount of money from
quarters will be (0.25)*3*N = 0.75N.
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Now we need to find the total amount of money from nickels, dimes, and quarters by adding
these three amounts and setting it equal to $20.  In equation form this is:
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0.05*N + 0.2*N + 0.75*N = 20
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Add the three terms on the left side. They total 1.0*N  so the equation becomes:
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1.0*N = 20
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Divide both sides by 1.0 and you get N = 20
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So there are 20 nickels.  
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Therefore the number of dimes is twice the number of nickels, so there are 40 dimes.
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And the number of quarter is three times the number of nickels, so there are 60 quarters.
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Now let's check it out. 20 nickels is $1.00. 40 dimes is $4.00. And 60 quarters (at 4 quarters
per dollar) is $15. This total is $1.00 + $4.00 + $15.00 = $20.00. The answer of 20 nickels,
40 dimes, and 60 quarters is correct.
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Hope this helps you to understand the problem and how you can get the answer.