On 6 September to 9 September, an average of 50 wafers were sold and from 10th September to 14 September, an average of 21 wafers were sold. $350 worth of wafers were sold from 15 September to 25 September. Given that a wafer was sold for $2, find the average number of wafers sold from 6 September to 25 September.
Number of wafers sold from 15 September to 25 September
= 350 ÷ 2
= 175

Number of days from 6 September to 9 September
= 9 - 6 + 1
= 4

Number of days from 10 September to 14 of September
= 14 - 10 + 1
= 5

Total number of wafers sold
= (4 x 50) + (5 x 21) + 175
= 200 + 105 + 175
= 480

Number of days from 6 September to 25 September
= 25 - 6 + 1
= 20

Average number of wafers sold
= 480 ÷ 20
= 24

Answer(s): 24