A is 30% more efficient than B. How much time will they, working together, take to complete a job which A alone could have done in 23 days? Choices
A) 11 days
B) 13 days
C) 20 3 / 17 days
D) 21 days
E) none of these

Rationale: "explanation : ratio of times taken by a and b = 100 : 130 = 10 : 13 suppose b takes x days to do the work . x = ( 23 * 13 ) / 10 = 299 / 10 a ' s 1 day work = 1 / 23 ; b ' s 1 day work = 10 / 299 ( a + b ) ' s 1 day work = ( 1 / 23 + 10 / 299 ) = 1 / 13 a and b together can complete the job in 13 days . answer is b"
Answer: B