## Histograms don't need a vertical scale## A vertical scale is often provided to help finding %s of areas## In a histogram the hight of a block represents CROWDING -- % per horizontal unit## DENSITY SCALE = % / hor.unit## with the DENSITY SCALE, areas come out in %s## AREA (%) = WIDTH (hor.unit) * HIGHT ( % / hor.unit )## Notice that hor.unit's cancel out.## Find the HIGHT of a block with## HIGHT = (AREA %) / (WIDTH hor.unit)## Consider the following example:A histogram of wages for part-time employees is shown below with the hights of the blocks (in the density scale) marked in parenthesis. Nobody earned more than $1,000 a month. The block from $200 to $500 is missing.## How tall should the missing block be? |

> ANSWER:

## The hights of the blocks are given in the DENSITY SCALE of % per $100. Hence, the areas of the blocks come out in %s.## The areas of the first two blocks are then: 10% and 20% resp.## The area of the last block is:## 5 ($100) * 5(%/$100) = 25 %## The 3 blocks together give (10+20+25)% = 55 %## The missing block must have an area of (100% - 55%) = 45%## The HIGHT of the missing block is then:## HIGHT = 45% / (3 $100) = 15 (%/$100) |

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Carlos Rodriguez <carlos@math.albany.edu> Last modified: Sat Feb 13 07:26:16 EST 1999