A new reading joins the set
A sixth seed tray is found behind the cupboard. Does it raise the mean or lower it?
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- Five trays: 20, 22, 24, 26, 28. Mean 24.
- A sixth tray joins at 30. Mean moves to 25.
Compare it with the mean you have now
It depends on the shoots (young green stems) in the new tray. A tray with more shoots than the mean raises the mean. A tray with fewer shoots lowers it.
Five trays hold 20, 22, 24, 26 and 28 shoots. They add to 120, and 120 ÷ 5 = 24. So the mean is 24. Add a sixth tray of 30 shoots. The total is 120 + 30 = 150 over six trays. Now 150 ÷ 6 = 25. The mean rose from 24 to 25.
Rule: Compare the new reading with the current mean. A reading above the mean raises the mean. A reading below the mean lowers it. A reading equal to the mean changes nothing.
In the lab, slide the new reading. Above 24, the mean rises. Below 24, the mean falls. At 24, the mean stays.
A stall's takings are the money it receives. Over five days, the mean is ₹620 a day. The five days add to 5 × 620 = ₹3,100. The sixth day's takings are ₹500. That is below ₹620, so the mean falls. The new total is ₹3,600 over six days, and 3,600 ÷ 6 = ₹600.