She blurted out the answer, but there is a little strategy to it:
Break it into prime factors:
1100 = 2*2*5*5*11
Take both 2's as one factor, 2*2=4
Take both 5's as one factor, 5*5=25
Take the 11 as the third factor = 11
1100 = 4*25*11
Bu taking all of each prime factor together, you keep any of the
other factors from having that prime factor in common with it.
Edwin