The selling price would be $11.20.
40% = 40/100 = 0.4
The mark up is 40% of the cost; this means 40% of 8:
40% of 8 = 0.4(8) = 3.20
8 + 3.20 = 11.20
Answer: the observer should consider to eliminate or to retake the third measure.
Explanation:
The four measures taken are 124.53, 124.55, 142.51 and 124.52.
As it can be easily seen, the third measure is much different from the other three. This means that something went wrong during the observation: it can be either the measure taken wrong or that the number was written wrong (if you switch the 2 and the 4 you get a number similar to the other ones).
If the third measure is not considered, an estimate of the mean would place it around 124.5, while if the outlier (the detatched number) is considered an estimate of the mean would increase to about 129.
Therefore, in order to obtain a more reliable mean, the observer should consider to eliminate or to retake the third measure.
1/10 the value of 237 means we must multiply 1/10 by 237
1/10 * 237 = 23.7
Hope this helps!
distance of a point 
from origin is $\sqrt{x^2+y^2}$
so distance is $\sqrt{(-15)^2+(8)^2}=\sqrt{225+64}=\sqrt{289}=17$
