1) Use unitary method for simple problems
e.g If A can complete a unit of work in 10 days, how many days can A do two units of work working at half the efficiency?
1 unit in 10 days
2 units in x days
i.e. x = 20
with full efficiency - 20 days
with 1/2 efficiency - y days
so logically, it should be double the time i.e. 40 days
2) Slightly complex problems - use
(1/x + 1/y = 1/Time) Below example explains how this formula can be derived.
e.g. If A can do something in 3 hours and B can do the same in 2, how long would it take them while working together?
A can do 1 unit in 3 hours
A can do x units in 1 hours
So x = 1/3
Similarly, B can do 1 unit in 2 hours
B can do y units in 1 hours
So y = 1/2
In one hour, total work = work done by A + work done by B
i.e. 1/3 + 1/2
Again, unitary method
5/6th work can be done in 1 hour
1 work (i.e. full) can be done in x hours
i.e. x = 6/5
Instead of using this method, just plug in the values in the formula.
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