On 4 June to 7 June, an average of 42 mangosteens were sold and from 8th June to 12 June, an average of 21 mangosteens were sold. $321 worth of mangosteens were sold from 13 June to 23 June. Given that a mangosteen was sold for $3, find the average number of mangosteens sold from 4 June to 23 June.
Number of mangosteens sold from 13 June to 23 June
= 321 ÷ 3
= 107

Number of days from 4 June to 7 June
= 7 - 4 + 1
= 4

Number of days from 8 June to 12 of June
= 12 - 8 + 1
= 5

Total number of mangosteens sold
= (4 x 42) + (5 x 21) + 107
= 168 + 105 + 107
= 380

Number of days from 4 June to 23 June
= 23 - 4 + 1
= 20

Average number of mangosteens sold
= 380 ÷ 20
= 19

Answer(s): 19