The distance between Exeter and London is $$175$$ miles. Sam left Exeter at $$10:00$$ on Tuesday for London. Morgan left London for Exeter at $$13:00$$ the same day. They travelled on the same road. Up to the time when they met, Sam\textquotesingle s average speed was $$25$$ miles per hour, and Morgan\textquotesingle s average speed was $$35$$ miles an hour.  At what time did Sam and Morgan meet? 
Overseas Competition->Knowledge Point->Word Problem Modules
Sam left Exeter three hours before Morgan left London, and travelled $$3\times 25$$ miles $$=75$$ miles in the three hours to $$13:00$$. So at $$13:00$$, the distance between Sam and Morgan was $$ \left( {175-75} \right) $$ miles $$=100$$ miles.  Let the time in hours between $$13:00$$ and the time at which Sam and Morgan met be $$t$$.  Then $$25t+35t=100$$. So $$t=\frac{{100}}{{60}}$$ hours $$=100$$ minutes $$=1$$ hour $$40$$ minutes. So Sam and Morgan met at $$14:40$$. 