"Mi hermano va a muchos conciertos en el verano."
Translation:My brother goes to a lot of concerts in the summer.
"My brother goes to a lot of concerts in the summer" is considered wrong on 7/19/18, not sure why
I just answered the with exact translation as yours on 8/13/18 and it was marked correct
Because mucho is an adverb that means "much / a lot" whereas muchos is an adjective that means "many / a lot of".
A little off topic, but would "Mi hermano va a muchos conciertos por el verano" mean the same (and also be correct)?
Although por la mañana is pretty common, you don't see por el verano very much. And there's actually a reason for that! It's because there really is a difference between en and por.
En is used to punctuate the period. You might start work at 5am en la mañana. You may have various meetings en la tarde or see several concerts en el verano.
Por is more encompassing. We generally sleep at night, but really through the whole night---so it's por la noche. Does he have to work tomorrow? Yes, por la tarde---the activity is assumed to take much of the afternoon. If you have a summer job, you work por el verano. Spending this winter down south? You'll be going there por (for/throughout) el invierno.
But you don't go to many concerts for the summer---so por would be wrong here.
Ah, now I see. Actually it would be pretty difficult to go to even one concert for the whole summer. Thanks!