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Alison, New Zealand
Friday, December 1, 2023
"If the mean average of 20 gifts is 50 pounds then the total of the 20 gifts will be 20 x 50 = 1000 pound. Assuming that one of the gifts is allowed to be free (0 pounds - is this counted as a whole number of pounds?) then, the cheapest 19 gifts would total the sum of the consecutive whole numbers from 0 to 18. This total can be worked out using the formula (0.5n^2 - 0.5n), or .5 x 19 x 18 = 171 pounds. The most expensive will therefore be 1000 - 171 = 829 pounds.
If the cheapest present is not allowed to be free and is therefore 1 pound, then the cheapest 19 gifts would total the sum of the consecutive whole numbers from 1 to 19. This total can be worked out using the formula (0.5n^2 + 0.5n), or .5 x 19 x 20= 190 pounds. The most expensive will therefore be 1000 - 190 = 810 pounds.
The 19 cheapest gifts are £1 to £19 then the most expensive is 1000 - sum of 1 to 19.
The 1000 is because of 20 x 50.
But you knew all that.
Sunday, December 3, 2023
"The 20 presents cost a total of 20x50= 1000 pounds
The cheapest 19 presents cost 19 x 20/2 = 190 pounds.
Meaning the most expensive present can cost 1000 - 190= 810 pounds.
Hope I did not miss anything.
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