Point A altimeter reading: +450
Point B altimeter reading: -50
<span>C. No, because although the results differ among the four surveys, the sample method used for all was the same. Luc RANDOMLY selects 40 students in every survey. Random selection in surveys do not create bias and the results are highly credible. This is because there are no preconceived notions or factors that affect the responses of people being surveyed.</span>
The desired number is the difference between the number of messages sent by the 16th day and the number sent by the 9th day:
... n = t(16) - t(9)
... n = (40×√16) - (40×√9)
... n = 40×(4 - 3) = 40
40 text messages were sent between the ninth and sixteenth day of the month.
Here, Just substitute their values,
4x + 3y
= 4(3) + 3(6)
= 12 + 18
= 30
In short, Your Answer would be 30
Hope this helps!