In a small workshop 5 people earn ₹18,000 a month each, 3 earn ₹26,000 each and 2 earn ₹40,000 each. What is the average monthly earning of the ten of them?

The three bands pay $5\times 18,000$ = ₹90,000, $3\times 26,000$ = ₹78,000 and $2\times 40,000$ = ₹80,000, a monthly wage bill of ₹248,000 shared by 10 people, so the average is 248000/10 = ₹24,800. ₹28,000 is the plain average of the three band figures, 84000/3, which counts a band paying two people as heavily as one paying five. ₹26,000 is the middle band, and the middle of three bands is not the average of ten people. ₹31,400 attaches the head counts to the wrong bands, putting 5 people on ₹40,000 and 2 on ₹18,000.