G is twice as fast as S in doing work. If G can do a work in 30 days less than S, how many days will they take to complete the work together?
Ratio of efficiency of G and S = 2 : 1
Ratio of time taken by G and S = 1 : 2
diff = 1 unit and 1 unit = 30
Time taken by G = 30 days and time taken by S = 60 days
Together they can complete in = $$\frac{1}{30}+\frac{1}{60}=\frac{90}{30\times\ 60}=\frac{1}{20}=20$$ days.
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