Angela bought 10 stamps that cost $1 or $1.20. Altogether, her total was $11. How many of each $1 stamps and how many of
each $1.20 stamps did she buy?

Let the first equation be x + y = 10

x = 10 -y

2nd equation will be 1x + 1.2y = 11

Substituting in 2nd equation

(10 - y) + 1.2y = 11

10 - y + 1.2y = 11

.2y = 1

y = 5

If y = 5, x = 5: coz x + y = 10

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.