Answer: 23
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Step-by-step explanation
Let's confirm the claim that the original mean is 24.
First we add the values:
12 + 30 + 19 + 27 + 21 + 35 = 144
Then divide this over the sample size (aka the number of values). The sample size is 6.
144/6 = 24
We have confirmed the mean of {12,30,19,27,21,35} is indeed 24.
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Next, let's introduce the value 17 to this list
We now have {12,30,19,27,21,35,17}
Add up the values
12 + 30 + 19 + 27 + 21 + 35 + 17 = 144 + 17 = 161
Then divide over the new sample size (which is now 7)
161/7 = 23
The new mean is 23
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Extra info: The old mean (24) decreased by 1 to get the new mean (23). This is because the new value we introduced (17) is less than the old mean. The new value will give a so called gravitational pull on the mean to make it smaller.