'Let me know' vs 'Let me knowing'

[Ojur]

Common Errors in English, Advanced Level

ESL/EFL Test #4 "Not the slightest idea", question 3

Let me knowing when you come back from your holidays so that we can make arrangements to meet.

(a) knowing
(b) come
(c) make
(d) to meet

Common Errors in English, Advanced Level

ESL/EFL Test #4 "Not the slightest idea", answer 3

Let me know when you come back from your holidays so that we can make arrangements to meet.

Correct entry: know
The error was: (a) knowing
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why not knowing?

Ojur

[Mister Micawber]

.
'Let' takes only the bare infinitive: 'let someone do/go/know/' etc.
.
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Native English teacher at Mister Micawber's