'surprised at how many' instead of 'surprised how many'

[Ljiljan Maksimovich]

English Grammar Tests, Elementary Level

ESL/EFL Test #90 "Using Make and Do (1)", question 1

The manager was surprised at how many things Ron could ......... at once.

(a) make
(b) do
(c) made
(d) did

English Grammar Tests, Elementary Level

ESL/EFL Test #90 "Using Make and Do (1)", answer 1

The manager was surprised at how many things Ron could do at once.

Correct answer: (b) do

Your answer was: correct
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Why should we use "surprised at how many..." instead of "surprised how many..."?

Thanks
Ljiljan

[Alan]

Hi Ljiljan,

Both surprised how and surprised at how are acceptable.

Alan
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English as a Second Language
You can read my ESL story Word Story: Health