Question 1047202
The {{{ A }}} = amount he had in the beginning
{{{ m }}} = the cost of a magazine
{{{ b }}} = the cost of a book
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(1) {{{ A = 4m + 3b }}}
(2) {{{ A = 2m + b + 84 }}}
(3) {{{ m = (1/3)*b }}}
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(3) {{{ b = 3m }}}
and
(1) {{{ A = 4m + 3*(3m) }}}
(1) {{{ A = 13m }}}
and
(2) {{{ A = 2m + 3m + 84 }}}
(2) {{{ A = 5m + 84 }}}
Plug (1) into (2)
(2) {{{ 13m = 5m + 84 }}}
(2) {{{ 8m = 84 }}}
(2) {{{ m = 10.5 }}}
and
(3) {{{ b = 3m }}}
(3) {{{ b = 3*10.5 }}}
(3) {{{ b = 31.5 }}}
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(1) {{{ A = 4m + 3b }}}
(1) {{{ A = 4*10.5 + 3*31.5 }}}
(1) {{{ A = 42 + 94.5 }}}
(1) {{{ A = 136.5 }}}
He started with $136.50
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check:
(2) {{{ A = 2m + b + 84 }}}
(2) {{{ A = 2*10.5 + 31.5 + 84 }}}
(2) {{{ A = 21 + 115.5 }}}
(2) {{{ A = 136.5 }}}
OK