Question 1027624
Let {{{ p }}} = the original price
The sale price is:
{{{ p - .2p }}}
{{{ p*( 1 - .2 ) }}}
{{{ .8p }}}
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First, I will ask: what fraction {{{ x/100 }}}
should I multiply the sale price by 
and then add to {{{ .8p }}} to
get back to {{{ p }}} ?
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{{{ ( x/100 )*( .8p ) + .8p = p }}}
I can divide both sides by {{{ p }}}
{{{ .8*( x/100 ) + .8 = 1 }}}
Divide both sides by {{{ .8 }}}
{{{ x/100 + 1 = 1.25 }}}
{{{ x/100 = .25 }}}
{{{ x = 25 }}}
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A 25% increase after the sale price is needed
to return to the original price
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check answer:
Suppose original price was $1200
{{{ .8*1200 = 960 }}}
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Now a 25% increase means factoring by {{{ 1.25 }}}
{{{ 1.25*960 = 1200 }}}
OK