this is combined variation

if q varies directly as b and inversely as c, and if q=0.2 when b=16 and c=8 find q when b=2 and c=5

and

if t varies directly as s and inversely as v-squared and if t= 0.1 when s=72 and v=6 find s when t=5 and v=0.2

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- Jan 31st 2006, 04:35 AM #1

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## help(urgent)

this is combined variation

if q varies directly as b and inversely as c, and if q=0.2 when b=16 and c=8 find q when b=2 and c=5

and

if t varies directly as s and inversely as v-squared and if t= 0.1 when s=72 and v=6 find s when t=5 and v=0.2

- Jan 31st 2006, 05:01 AM #2

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- Jan 31st 2006, 08:01 AM #3

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Originally Posted by**machilove**

$\displaystyle q=k\times b$

Now when $\displaystyle q=0.2$, $\displaystyle b=16$, so:

$\displaystyle 0.2=k \times 16$,

so:

$\displaystyle k=0.2/16=1/80$,

so when $\displaystyle b=2$ we have:

$\displaystyle q=2/80=1/40$.

if $\displaystyle q$ varies inversely as $\displaystyle c$ then there is a constant $\displaystyle m$ such that:

$\displaystyle q=m/c$

Now when $\displaystyle q=0.2$ $\displaystyle c=8$, so:

$\displaystyle 0.2=m/8$,

so:

$\displaystyle m=1.6$.

Hence when $\displaystyle c=5$ $\displaystyle q=1.6/5=8/25$.

RonL