All adverbs ending in -ly and certain other adverbs,especially long ones, form the comparative by the addition of the word more orless. Some short or irregular adverbs, however, form the comparative by the additionof the ending -er.
The experiment went better than expected.[well changed to comparative form better with ending -er]
We got our results more quickly than we expected. [comparative with more]
The solution reached equilibrium less rapidly than we thoughtit would. [comparative with less]
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