statistics

-A set of seven scores has a mean of 10. If one of the scores is changed from X=15 to X=1, what will be the new value for the new mean?

-A sample of n=8 scores has a mean of M=12. One new score is added to the same and the new mean is found to be M=13. What is the vaule of the new score?

What steps do I follow to figure out these types of problems? I don't quite understand how the book is explaining it.

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  1. If a set of seven numbers has a mean of 10, then the sum of the ten numbers must be 70. If you raise one of thme from 1 to 15, than the total becomes 84. Divide that by 7 for the new mean value.

    Use a similar approach for the second question. The total for the first 8 numbers is 8x12 = 96. When a ninth number is added, the total becomes 9x13 = 117. How much did the thirteenth number add to the total?

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