先生に急に当てられて、トンチンカンな答えをしてしまった。

tbd

I gave an answer that was way out in left field when the teacher caught me off-guard and called on me.

私の祖父は耳が遠いので、よくトンチンカンな返事をする。

tbd

My grandfather, being hard of hearing, often makes an irrelevant answer.