Every frugal shopper counts his or her coupons before they shop.
Explanation:
In the above sentence, the pronoun used would be 'his' or 'her' which would agree with the number of the antecedent. The antecedent is 'every frugal shopper' which is singular in number and hence, the pronoun used would be singular. The statement has a pronoun agreement error.
The only thing I can think of would be the numbers on mailboxes or apartment doors (address numbers). Those are the only numbers I imagine you would be seeing on houses and things but I am not 100% sure of this answer.
