GWD 10 Q10

Q10:

A certain quantity is measured on two different scales, the R-scale and the S-scale, that are related linearly.  Measurements on the R-scale of 6 and 24 correspond to measurements on the S-scale of 30 and 60, respectively.  What measurement on the R-scale corresponds to a measurement of 100 on the S-scale?

A.     20

B.     36

C.     48

D.     60

E.      84

 不懂题意，请指教，答案是C

because the R-scale and the S-scale are related linearly, so we can make a equation like this:  S=kR+B (where B is a constant), according to the known figures, we get: 30=6k+B and 60=24k+B, and thus geting the result of k=5/3 and B=20.  the last step, 100=5R/3+20=> R=48