Rocky can walk a certain distance in 40 days when he rests 9 hours a day. How long will he take to walk twice the distance, twice as fast and rest twice as long each day?
Answer
Answer (as printed):
Explanation
Let the distance in the two cases be y and 2y respectively and the speed be z and 2z respectively. Let the required number of days be x. More distance, More days (Direct Proportion) More speed, Less days (Indirect Proportion) More resting time, More days (Direct Proportion) Distance y : 2y Speed 2 z : z : : 40 : x Resting time 9 : 18 2 y × z × 18 × 40 \ y × 2z × 9 × x = 2y × z × 18 × 40 ⇒ x = = 80. y × 2z × 9 Hence, required number of days = 80.
Explanation as extracted from the printed page; notation may be imperfect.