Question 1079325
Let {{{ a }}} = number in psych class
Let {{{ b }}} = number in art history class
Let {{{ c }}} = number in algebra class
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(1)
{{{ a = 3b }}}
(2)
{{{ c = b + 13 }}}
(3)
{{{ a + b + c = 78 }}}
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Substitute (1) and (2) into (3)
{{{ a + b + c = 78 }}}
{{{ 3b + b + b + 13 = 78 }}}
{{{ 5b + 13 = 78 }}}
{{{ 5b = 65 }}}
{{{ b = 13 }}}
and
{{{ a = 3b }}}
{{{ a = 3*13 }}}
{{{ a = 39 }}}
and
{{{ c = b + 13 }}}
{{{ c = 13 + 13 }}}
{{{ c = 26 }}}
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There are 39 in psych class
There are 13 in art history class
There are 26 in algebra class
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check:
{{{ a + b + c = 78 }}}
{{{ 39 + 13 + 26 = 78 }}}
{{{ 78 = 78 }}}