If 0<r<1<s<2 , which of the foll must be less than 1??

(1)r/s
max value of r can be .99, min value of s can be 1.01

so .99 /1.01 < 1 hence this would always be less than 1

(2)rs

r =.5 s =1.2 so rs =.6<1

r=.9 s =1.8 rs =1.62>1 NOT SUFF

(3)s-r

s=1.2 r =.8 s-r =.4<1

s=1.9 r =.1 s-r =1.8 >1

not suff

so I only

I dont know why but when I took values like 1/2 , 1/3 , 1/4 and so on for R and 3/4 , 5,4 and 7/6 for S every one of the answer choices were less than 1...But your approach is simple and easy..Thank you