A) 30 days
B) 50 days
C) 75 days
D) 80 days
Correct Answer: A
Solution :
A's 1 days' work \[=\frac{1}{80}\] A's 10 days' work \[=\frac{10}{80}\,=\frac{1}{8}\] Remaining work \[=1-\frac{1}{8}\,=\frac{7}{8}\] \[\frac{7}{8}\] of the work is completed by B in 42 days. \[\therefore \] The whole work is completed by B in \[\frac{42\times 8}{7}\] days = 48 days \[\therefore \] B?s 1 days work \[=\frac{1}{48}\] (A + B)?s 1 days work \[=\frac{1}{80}+\frac{1}{48}\] \[\therefore \] A and B can complete the whole work together in 30 days.
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