Question 494811
At his usual speed:
(1) {{{ d = r*t }}}
At his slower rate,
(2) {{{ d = (6/7)*r*(t + 25) }}}
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Substitute (1) into (2)
{{{ r*t = (6/7)*r*(t + 25) }}}
{{{ 7r*t = 6*r*(t + 25) }}}
{{{ 7r*t = 6r*t + 150r }}}
Divide through by {{{r}}}
{{{ 7t = 6t + 150 }}}
{{{ t = 150 }}}
His usual time is {{{ 150 }}} min
or {{{ 150/60 }}} = 2 and 1/2 hours