Question 1072760
Let {{{ s[1] }}} = Tracy's speed in laps / sec
Let {{{ s[2] }}} = Kelly's speed in laps / sec
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{{{ s[1] = 1/45 }}} laps/sec
Let {{{ x }}} = the fraction of a lap that That Tracy
covers in {{{ 20 }}} sec
{{{ 1 - x }}} = the fraction of a lap that Kelly covers
in {{{ 20 }}} sec
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Tracy's speed is:
{{{ s[1] = x/20 }}}
and
{{{ 1/45 = x/20 }}}
{{{ x = 4/9 }}}
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And Kelly's speed is:
{{{ ( 1 - x )/20 = ( 1 - 4/9 ) / 20 }}}
{{{ ( 5/9 )/20 = 1/36 }}}
So Kelly completes 1 lap in 36sec
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check answer:
{{{ s[1] = x/20 }}}
{{{ s[1] = (4/9)/20 }}}
{{{ s[1] = 1/45 }}}
and
{{{ s[2] = 1/36 }}}
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Think of one of them standing still and the other
moving at the sum of their speeds
{{{ 1 = ( 1/45 + 1/36 )*20 }}}
{{{ 1 = ( 4/180 + 5/180 )*20 }}}
{{{ 1 = ( 9/180 )*20 }}}
{{{ 1 = (1/20)*20 }}}
{{{ 1 = 1 }}}
( 1 lap finished in 20 sec )
OK