Question 736645
(1) {{{ 10d + 25q = 180 }}} ( in cents )
(2) {{{ q = 2d }}}
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(1) {{{ 10d + 25q = 180 }}} 
(2) {{{ d = q/2 }}}
Substitute (2) into (1)
(1) {{{ 10*(q/2) + 25q = 180 }}} 
(1) {{{ 5q + 25q = 180 }}}
(1) {{{ 30q = 180 }}}
(1) {{{ q = 6 }}}
and
(2) {{{ d = q/2 }}}
(2) {{{ d = 6/2 }}}
(2) {{{ d = 3 }}}
There are 3 dimes
check:
(1) {{{ 10*3 + 25*6 = 180 }}}
(1) {{{ 30 + 150 = 180 }}}
(1) {{{ 180 = 180 }}}
OK