Three monomers of glucose (C6H12O6) are bonded together by condensation to form oligosaccharide.

Three monomers of glucose (C6H12O6) are bonded together by condensation (dehydration) reactions to form an oligosaccharide. The new molecular formula is?

The Answer is C18H32O16.

I am confused about how this is the answer.

When 2 molecules are hooked together by dehydration synthesis, a molecule of water is removed from between them. So when 2 molecules of glucose are hooked together, 2 x C6H12O6 = C12H24O12, but you have to take away H2O, which leaves C12H22O11 for the disaccharide. For the trisaccharide, another H2O is removed, resulting in C18H32O16.

The summary would be 3 C6H12O6 ---> C18H32O16 2 H2O