Homework Problem 2, STAT 705, Fall 2017.

Assigned 8/31/2017,  Due Monday 9/11/2017

Access the data-set  "nepali"  within the R package "faraway", which contains 
information about children (at various ages, which I think must be measured in 
months) and their mothers. See the web-page brought up by the command 
"help(nepali)" for details on the data-frame "nepali" you will see by loading 
the "faraway" R package onto your computer.

Answer the following questiond sbout the dataset, giving R code lines to show 
how you obtained the answers. (You will not get credit for the answers without 
the associated code lines, together with some intermediate results as appropriate 
to indicate that your code lines did give the corrct desired answer.)

(a) How many unique children (i.e., ID's) are represented in the dataset ?

(b) How many unique households are represented in the dataset ?

(c) Some of the observations on children are missing the height ("ht") or weight ("wt")
data. Are there any observations missing one but not both of these data fields ?

(d) Are there any other missing observations in the dataset ?

(e) From the logic of the dataset, it seems likely but not certain that the 
data-fields on the mother ("mage", "lit","died","alive") should be constant 
for all records within each household. Is this true in the "nepali" datset ?

In how many households was there some change in one of the mother data-fields 
across all records in the dataset ?

(f) Give a summary or histogram of the set of earliest ages for the mother 
in each distinct household in the dataset.