If the cost of a telephone conversation varies directly as the length of the time of conversation, and if the cost of six minutes is $0.90, what would be the cost for a nine-minute call?

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Answer 1 · 2018-08-05T09:48:13

Cost for a $9$ minute call is $$1.35$

Let length of time be $t$ minutes and cost is $$c$ , then,

$c prop t or c = kt or k = c/t; k$ is variation constant.

$t= 6 , c =$0.90:. k = 0.90/6=0.15$ , therefore, variation

equation is $c = 0.15 t ; t= 9 , c= ? c =0.15*9=$1.35$

Cost for a $9$ minute call is $$1.35$ [Ans]

Answer 2 · 2018-08-05T14:06:29

Cost = $$1.35$

As the cost is proportional to the time you can set up a direct proportion using equivalent fractions:

$6/0.90 =9/x" "(larr "minutes")/(larr "cost")$

$x = (9xx0.90)/6$

$=1.35$