The average score of 30 students is 70. When the students with scores 60 and 65 leave and three new students join in, the average remains unchanged. What is the average score of those three new students?

The total score of the initial 30 students is 30 x 70 = 2100. When two students scoring 60 and 65 leave, the remaining sum is 2100 - 125 = 1975. Let the average of the three new students be Y, so the new total score becomes 1975 + 3Y; because the new average of the 31 students is still 70, the new total score must be 31 x 70 = 2170. Solving 1975 + 3Y = 2170 gives 3Y = 195, so the average score of the three new students is 65.

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