# Chapter 6 - Systems of Equations and Inequalities - Mid-Chapter Quiz - Page 389: 15

$.05n +.1d = 1.7$ $d+n = 21$ Substitution is used since it is easy to substitute one variable for another (in the other equation). $d=13$ $n=8$

#### Work Step by Step

d= # dimes, n = # nickels $.05n +.1d = 1.7$ $d+n = 21$ $d+n = 21$ $d+n -n= 21-n$ $d = 21-n$ $.05n +.1d = 1.7$ $d = 21-n$ $.05n +.1d = 1.7$ $.05n +.1(21-n) = 1.7$ $.05n+ 2.1 -.1n = 1.7$ $-.05n + 2.1 = 1.7$ $-.05n + 2.1+.05n-1.7 = 1.7+.05n-1.7$ $.4 = .05n$ $.4/.05 = .05n/.05$ $8 =n$ $d+n = 21$ $d + 8 = 21$ $d +8-8 = 21-8$ $d = 13$

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