Question 839154
Let {{{ a }}} = amount in billions spent on newspaper ads
Let {{{ b }}} = amount in billions spent on TV ads
Let {{{ c }}} = amount in billions spent on radio ads
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(1) {{{ a + b + c = 86.9 }}}
(2) {{{ b + c = a + 2.7 }}}
(3) {{{ a = b + 5.5 }}}
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There are 3 unknowns and 3 equations
so it is solvable
Substitute (2) into (1)
(1) {{{ a + a + 2.7 = 86.9 }}}
(1) {{{ 2a = 86.9 - 2.7 }}}
(1) {{{ 2a = 84.2 }}}
(1) {{{ a = 42.1 }}}
and
(3) {{{ 42.1 = b + 5.5 }}}
(3) {{{ b = 42.1 - 5.5 }}}
(3) {{{ b = 36.6 }}}
and
(1) {{{ 42.1 + 36.6 + c = 86.9 }}}
(1) {{{ c = 86.9 - 78.7 }}}
(1) {{{ c = 8.2 }}}
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42.1 billion was spent on newspaper ads
36.6 billion was spent on TV ads
8.2 billion was spent on radio ads
check:
(2) {{{ b + c = a + 2.7 }}}
(2) {{{ 36.6 + 8.2 = 42.1 + 2.7 }}}
(2) {{{ 44.8 = 44.8 }}}
OK -you can check the other 2 equations