$1)$Find the variance for the set of data:$23,31,14,21,21$

$2)$find the trade discount of computer that lists for $$1000$ if a discount rate of $45\%$ is offered?

$3)$find the net price of a computer that lists for $$280$ if a discount of $40\%$ is offered.

$4)$ calculate the trade discount for $30$ boxes of computer paper if the unit price is $$15\mathrm{.}95$ and a single trade discount is rate of $25\%$ is allowed.

$6)$ one manufcator needs to claculate the net price of an order with a list price of $$600$ and a trade discount series of $12/9/5.$ Use the net decimal equivalent to find the net price.