Please help: r varies directly as s and t; r = 29 for....

[P.Gallegos]

Find an equation of joint variation. Then solve for the missing value.

r varies directly as s and t. One set of values is r=28, s=7, t=8. Find r when when s=12 and t=9.[/b]

[ibueno1]

you should try to use this formula r=k*s*t and substitute the numbers into it i hope this helps you :D :D

[JOSE JAIME-RODRIGUEZ]

The formula r=k*s*t will look like this once you plug in the numbers from your problem:28=k*7*8

Hope this helps get you started!!! 8-)

_____________
JOSE

[stacey elias]

substitute r,s,t
r=28,s=7,t=8
28=k*7*8
then you multiply both sides by 1/56
1/2 k
r=1/2st
then substitute r=1/2st
r=1/2*12*9
do you know how to finish it now.

[stapel]

Please review the replies to this almost-identical (http://www.freemathhelp.com/forum/viewtopic.php?t=14529) exercise.

If you get stuck, please reply showing your work. Thank you.

Eliz.