Harry and Ron can individually build a castle in 20 days and 30 days r

Solution

• We are given:


o Time taken by Harry to build the castle \(= 20\) \(days\).
o Time taken by Ron to build the castle \(= 30\) \(days\).

• Let us assume the work to be \(60\) \(units\) (LCM of 20 and 30)


o Efficiency of Harry \(= \frac{60}{20} = 3\) units/day
o Efficiency of Ron \(= \frac{60}{30} = 2\) unit/day
• If they work together they can build the castle in \(= \frac{60}{(2+3)} = 10\) days.


o But they are working for only \(5\) \(days\).
o Hence they will complete only half of the work which is \(30\) \(units\).

• The remaining half (\(30 units\)) of the work is done by Hemione in \(5\) \(days\).
• Thus, Hermione can complete the total work in \(5*2 = 10\) \(days\).
• And the correct answer is Option B