What is the average of the six weights?

The average of five weights is 13 grams.This set of five weights is then increased by another weight of 7 grams. What is the average of the six weights?

Average Weight = $\dfrac{Total Wt}{5}$ = 13
Total Weight = 13 * 5 = 65
When another weight of 7 grams added Total weight = 65+7 = 72

Average Weight = $\dfrac{72}{6}$ = 12

Average of six weights is 12 gms.