If B takes x days, A takes x/1.3 days. We are given A takes 23 days, so B takes 23*1.3 = 29.9 days. Working together, their combined rate is 1/23 + 1/29.9. The time taken is 1 / (1/23 + 1/29.9) ≈ 13 days. [cite: 11556]