The mean daily wage of all 50 workers at a Rajkot workshop is ₹560. The 30 skilled workers among them have a mean daily wage of ₹620. Find the mean daily wage of the 20 unskilled workers.

Total wage bill $=560\times 50=28000$; the skilled workers account for $620\times 30=18600$, leaving $28000-18600=9400$ for the 20 unskilled workers, so their mean is $\frac{9400}{20}=₹470$. "500" assumes the two group means sit symmetrically about 560 (560 - 60); "940" divides 9400 by 10 (the difference 30 - 20) instead of by 20; "313.33" divides the remaining 9400 by 30 instead of 20.