# R notes for Activity 19-6: Backpack Weights

You can read the data and preview basic information with

```Backpack = read.csv("/home/rebelsky/Stats115/Data/Backpack.csv")
summary(Backpack)
tail(Backpack)
```

As you will find, there are 100 rows in the table, and three columns. The columns are labeled `BackpackWeight`, `BodyWeight`, and `Sex`.

## 19-6 b: A Ratio Vector

This question asks you to build a vector that represents the ratio of backpack weight to body weight. As you may recall, we can create that vector with

```Ratio = Backpack\$BackpackWeight/Backpack\$BodyWeight
```

You should be able to figure out the appropriate ways to display these data. If you'd like to get a histogram close to the one in the sample answers, you can use

```hist(Ratio,
breaks=seq(from=-0.008, to=0.20, by=0.015),
axes=FALSE,
main="",
xlab="Ratio of Backpack Weight to Body Weight"
)
axis(1, seq(from=0,to=0.2,by=0.02))
axis(2, seq(from=0,to=20,by=4))
```

## 19-6 c: Confidence Intervals

The authors recommend that you compute this confidence interval by hand. However, you may also use `t.test`.

Samuel A. Rebelsky, rebelsky@grinnell.edu

Copyright (c) 2007-8 Samuel A. Rebelsky.

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