For these 15 cars, the range of Selling Price was $15K and lowest was $4,5K. In June Tome sold 10 cars. Ranges was $16,5K and $6,1K lowest SP. What was the range of SP of the 25 cars Tom sold?

ans: $18,100.

I tried solving Range=g-l
=16,5-4,5
=$12K.

But $18,1 solution would be $12K +$6,1K and any manipulation incl. averaging the lowest/higest ranges does not give that result.

that's an entirely correct formula, but you applied it incorrectly: 'G' stands for greatest value and 'L' stands for least value. you plugged in the range for 'G' instead of 'range', so that's why your answer is incorrect.

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both unknowns are 'G', so solve for 'G':
G = L + range

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may:
range = 15
L = 4.5
G = 15 + 4.5 = 19.5

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june:

range = 16.5
L = 6.1
G = 16.5 + 6.1 = 22.6

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overall 'L' = 4.5 (lower of the two 'L's)
overall 'G' = 22.6 (higher of the two 'G's)
overall range = 22.6 - 4.5 = 18.1