A university investigated how much space on its computers' hard drives is used for data storage. The results are shown below. It is given that $40$ hard drives use less than $20 GB$ for data storage.

Compute total frequency and estimate the value of $k,$ if $25\%$ of the hard drives use $k GB$ or more.

The lengths of the $575$ items in a candle maker's workshop are represented in the histogram.

What proportion of the items are less than $25 \mathrm{cm}$ long?. Estimate the number of items that are between $12.4$ and $36.8 \mathrm{cm}$ long.

The thicknesses, $k \mathrm{mm},$ of some steel sheets are represented in the histogram. It is given that $k<0.4$ for $180$ sheets.

Find the ratio between the frequencies of the three classes. Give your answer in simplified form.

Find the value of $n,$ given that frequency density measures sheets per $n \mathrm{mm}.$

The thicknesses, $k \mathrm{mm},$ of some steel sheets are represented in the histogram. It is given that $k<0.4$ for $180$ sheets.

Find the value of $n,$ given that frequency density measures sheets per $n \mathrm{mm}.$
Calculate an estimate of the number of sheets for which:
$k<0.5$

The thicknesses, $k \mathrm{mm},$ of some steel sheets are represented in the histogram. It is given that $k<0.4$ for $180$ sheets.

Find the value of $n,$ given that frequency density measures sheets per $n \mathrm{mm}.$

Calculate an estimate of the number of sheets for which:
$0.75⩽k<0.94$

The thicknesses, $k \mathrm{mm},$ of some steel sheets are represented in the histogram. It is given that $k<0.4$ for $180$ sheets.

Find the value of $n,$ given that frequency density measures sheets per $n \mathrm{mm}.$
The sheets are classified as thin, medium or thick in the ratio $1 : 3 : 1.$
Estimate the thickness of a medium sheet, giving your answer in the form $a⩽k<b.$ How accurate are your values for $a$ and $b?$