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If the average of 7 numbers is 39, then the sum of these numbers is 7*39.
If the average of 3 numbers is 27, then the sum of these numbers is 3*27.
Then the sum of 4 (four) remaining numbers is the difference 7*39 - 3*27.
Then the average of these 4 numbers is = 48.
Answer. The average of these 4 numbers is 48.
Solved.
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I explained the solution in all details, so it took 4 lines.
But the person who is familiar with the subject, must solve such problems in ONE LINE:
The average of these 4 numbers is = 48.
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