Question

Determine whether quantities vary directly or inversely and find the constant of variation.
Liz is a jabber-mouth; she can speak 225 words in 5 minutes. At this rate, if she talks from 10:30 a.m. until 11:15 a.m., how many words will she speak? (Also say how many words she will say)

Thx!

Answer 1

This is a problem in direct variation.  For every five minutes that goes by, Liz utters 225 words.  The general form of an equation of direct variation is 

w = k x, where w is the # of words, k is the constant of proportionality and x is the number of minutes that have elapsed.

Find k by dividing 225 words by 5 minutes, to find the number of words per minute.

Next:  How many minutes are there between 10:30 a.m. and 11:15 a.m.?  Calculate w=kx, using your constant of proportionality, k, and that number of minutes.