If the store pays $2 for a Halloween mask and marks up the price by 35%, we can calculate the amount of the mark-up as follows:
Mark-up percentage = 35%
Cost of the mask = $2
Mark-up amount = Mark-up percentage x Cost of the mask
Mark-up amount = 0.35 x $2
Mark-up amount = $0.70
Therefore, the amount of the mark-up is $0.70. The store sells the Halloween mask for $2.70 ($2 + $0.70 mark-up).