Final answer:
The greatest common divisor of 18 and 28 is 2, indicating Ms. Lee can make 9 teams of 2 sixth graders and 2 seventh graders each. However, it's not possible to create equal-sized teams of 18 students each while maintaining equal numbers of sixth and seventh graders.
Step-by-step explanation:
The question is asking us to divide a group of chess club students into equal-sized teams with the same number of sixth graders and seventh graders. To do this, we need to find a number that both 18 (the number of sixth graders) and 28 (the number of seventh graders) can be divided by equally without any remainder. This is known as finding the greatest common divisor (GCD) of the two numbers.
By applying the Euclidean algorithm or listing the factors of both numbers, we discover that the greatest common divisor of 18 and 28 is 2. Therefore, Ms. Lee can make 9 teams, with each team having 2 sixth graders and 2 seventh graders.
However, the question asks for the number of equal-sized groups of 18 students Ms. Lee can make. Since we can only fit one pair of sixth and seventh graders (2 sixth graders + 2 seventh graders = 4 students) in a group of 18, this doesn't directly solve the stated problem. As such, we cannot form teams of 18 students each while maintaining equal numbers of sixth and seventh graders with the numbers given.