Answer: John had 72 pins originally.
Step-by-step explanation:
Let x represent the total number of pins that John had originally.
John divided his souvenir hat pins into two piles. The two piles had an equal number of pins. This means that each pile has x/2 pins.
He gave his brother one-half of one-third of one pile. This means that the number of pins that he gave his brother is
1/2 × 1/3 × x/2 = x/12 pins
The total amount left is
x/2 + (x/2 - x/12) = x/2 + 5x/12 = 11x/12
John had 66 pins left. Therefore
11x/12 = 66
11x = 66 × 12 = 792
x = 792/11 = 72
