3. (20 points) Young marketer Masha was supposed to survey 50 customers in an electronics store throughout the day. However, there were fewer customers in the store that day. What is the maximum number of customers Masha could have surveyed, given that according to her data, 7 of the respondents made an impulse purchase, 75% of the remaining respondents bought the product under the influence of advertising, and the number of customers who chose the product based on the advice of a sales consultant is one-third of the number who chose the product under the influence of advertising.
Answer: 47.

Solution: Let the number of customers surveyed be $x$. Then, the number of customers who made a purchase under the influence of advertising is $(x-7) \cdot 3 / 4$, and the number of customers who made a purchase on the advice of a sales consultant is $(x-7)/4$. Since the number of customers can only be an integer, $x-7$ must be divisible by 4. The maximum suitable number $x$, less than 50, is 47.