Final answer:
The overall percent correct in the contest is calculated by multiplying the number of people by the number of questions they got right and summing these numbers up. Dividing the total number of correct answers by total possible answers and converting to a percentage, we get 76.5%, which unfortunately doesn't match any of the answer choices provided in the question.
Step-by-step explanation:
To calculate the overall percent correct that everyone earned in this math contest, we have to consider the number of people who answered each set of questions correctly and the total number of questions. First, 15% of the 1000 people, which is 150 people, answered 12 questions correctly. Three-fifths of the participants, which is 600 people, answered 15 questions correctly. This leaves us with 250 people (since 1000 - 150 - 600 = 250) who answered 18 questions correctly.
To find the total number of questions answered correctly by all participants, we multiply the number of people by the number of questions they got right for each group and add these numbers together:
150 people x 12 questions = 1800 correct answers
600 people x 15 questions = 9000 correct answers
250 people x 18 questions = 4500 correct answers
The total number of correct answers is then 1800 + 9000 + 4500 = 15300 correct answers.
The total number of questions that could have been answered by all 1000 people is 20 questions per person, so that's 20 x 1000 = 20000 possible correct answers.
The percent correct for the entire contest is the total correct answers divided by the total possible correct answers, multiplied by 100 to get the percentage:
(15300 correct answers / 20000 possible answers) x 100 = 76.5%
However, this is not an answer choice provided in the question. Given the available options (A) 40%, (B) 45%, (C) 50%, (D) 55%, it is likely that there is a misunderstanding in the question or a typo, as none of these match the calculated percentage. Therefore, we would need further clarification to select the correct answer choice from the options given.