Question 597325
Let {{{ n }}} = number of nickels
Let {{{ d }}} = number of dimes
given:
(1) {{{ n = d - 10 }}}
(2) {{{ 5n + 10d = 310 }}} ( in cents )
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Substitute (1) into (2)
(2) {{{ 5n + 10d = 310 }}} 
(2) {{{ 5*( d - 10 ) + 10d = 310 }}} 
(2) {{{ 5d - 50 + 10d = 310 }}}
(2) {{{ 15d = 360 }}}
(2) {{{ d = 24 }}}
and, since
(1) {{{ n = d - 10 }}}
(1) {{{ n = 24 - 10 }}}
(1) {{{ n = 14 }}}
She has 14 nickels and 24 dimes
check:
(2) {{{ 5n + 10d = 310 }}}
(2) {{{ 5*14 + 10*24 = 310 }}}
(2) {{{ 70 + 240 = 310 }}}
(2) {{{ 310 = 310 }}}
OK