Question 508726
Let {{{ p }}} = number of pennies
Let {{{ n }}} = number of nickels
Let {{{ d }}} = number of dimes
given:
(1) {{{ d = 2p }}}
(2) {{{ n = 3p }}}
(3) {{{ 1*p + 5n + 10d = 180 }}} ( in pennies )
Substitute (1) and (2) into (3)
(3) {{{ p + 5*3p + 10*2p = 180 }}}
(3) {{{ p + 15p + 20p = 180 }}}
(3) {{{ 36p = 180 }}}
(3) {{{ p = 5 }}}
and
(1) {{{ d = 2p }}}
(1) {{{ d = 10 }}}
and
(2) {{{ n = 3p }}}
(2) {{{ n = 15 }}}
There are 5 pennies, 15 nickels, and 10 dimes
check answer:
(3) {{{ 1*p + 5n + 10d = 180 }}} 
(3) {{{ 5 + 5*15 + 10*10 = 180 }}}
(3) {{{ 5 + 75 + 100 = 180 }}}
(3) {{{ 180 = 180 }}}