Answer
$.05n +.1d = 1.7$
$d+n = 21$
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 $
$d+n = 21$
$d + 8 = 21$
$d +8-8 = 21-8$
$d = 13$
