11. An airplane flying against the wind travels 140 miles in the same amount of time it would take the same plane to travel 160 miles with the wind. If the wind speed is a constant 20 miles per hour, how fast would the plane travel in still air?

Plane speed x mph

wind speed 20 mph

against wind x - 20 mph

with wind x + 20 mph

Distance against wind 140

Distance with wind 160

Time = same equate the time against with time with current

t=d/r

140 /(x- 20 )= 160 /(x+ 20 )

140 *(x+ 20 )= 160 *(x- 20 )

140 x + 2800 = 160 x -3200

140 x -160 x = -3200 + -2800

-20 x = -6000

/ -20

x= 300 mph

introduction, methodology, results, discussion

step-by-step explanation:

an observational study is one which consists of actual observation to record data and then analyse the data.

there are a number of factors that should be analyzed before starting an observational study.

the main four factors are:

i) introduction:   this should be analysed to check whether the purpose of the study is correctly established and the data recorded are appropriate for the study

methodology:   the method of collecting the data, such as whether randomly selected, and whether sample size matches with the population to be studied, whether questions asked are easy to answer by common men, etc.

results: then results such as summary of data with comments should be studied thoroughly

discussion:   the last is the discussion, this can be either by management people or persons who are all interested , etc.

practice. practice. practice.