Jan=18,feb=25,mar=21,apr=16,mei=20. jika banyak buku tulis pada bulan januari 30lusin,berapa buku rata-rata banyak buku tulis yg terjual setiap bulannya!

18+25+21+16+20 = 100
Jan = 30
Feb = 25/18 x 30 = 25x5/3 = 125/3
Mar = 21/18 x 30 = 21/3 x 5 = 35
Apr = 16/18 x 30 = 16 x 5/3 = 80/3
Mei = 20/18 x 30 = 20 x 5/3 = 100/3

rata² = (30 + 35 + (125+80+100)/3)/100
= (65 + (305/3))/100
= (195+305)/3)/100
= 500/(3 x 100)
= 50.000/300
= 166⅔ buku