
Bad 

Bad at 

The use of the preposition in
in the first sentence is wrong. It should be replaced with
at. 
Incorrect 
The boy is bad in
Mathematics. 
Correct 
The boy is bad at
Mathematics. 



Worse
at, Worst at 

Similarly, the use of
in for the comparative
and the superlative of bad (worse and worst) is also wrong. 
Incorrect 
The boy's brother is worse in
Mathematics. 
Incorrect 
His friend is the worst in
Mathematics. 
Correct 
The boy's brother is worse at
Mathematics. 
Correct 
His friend is the worst at
Mathematics. 



Excel 

Excel
at ( an activity ) 

According to English Prepositional
Idioms by Frederick T. Wood, for being extremely good at an
activity, excel in may be used but excel at
is more common 
Incorrect 
This artist excels in
painting birds. 
Correct 
This artist excels at
painting birds. 



Excel in ( an
attribute or quality ) 

According to the same source, the use of the preposition at is not
appropriate when we use excel for qualities or attributes. 
Incorrect 
She excels at
intelligence. 
Incorrect 
My brother excels at
foreign languages. 
Correct 
She excels in
intelligence. 
Correct 
My brother excels in
foreign languages. 



Good 

Good at 

The use of the preposition
in in the first sentence
is wrong. The correct preposition to use is
at. 
Incorrect 
He is good in
Mathematics. 
Correct 
He is good at
Mathematics. 



Better
at, Best at


The use of the preposition
in for the comparative and
the superlative of good (better and best) in the two sentences is
wrong. 
Incorrect 
He is better in
Mathematics. 
Incorrect 
He is the best in
Mathematics 
Correct 
He is better at
Mathematics. 
Correct 
He is the best at
Mathematics 

