mankey wrote:The OG says "estimated to be" is the right idiom and not "estimated at".
this is one of those instances in which the OG explanation is inaccurate. (that happens infrequently, but not as infrequently as one might hope.)
fortunately, what's happening is pretty simple: "at" is a preposition, and so (like other prepositions) needs to have a
noun as its object.
"40 to 44 million years
old" is not a noun, so, wrong.
(if the sentence had said something like
The age of xxxx was estimated at 40 to 44 million years, then that version would be fine.)
as proof, consider the following from GMAT PREP:
With surface temperatures estimated at minus 230 degrees Fahrenheit, Jupiter's moon Europa has...
estimated at + noun ... again, no problem.
Ron has been teaching various standardized tests for 20 years.
--
Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions à Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi
--
Quand on se sent bien dans un vêtement, tout peut arriver. Un bon vêtement, c'est un passeport pour le bonheur.
Yves Saint-Laurent
--
Learn more about ron