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A) \[{\text{A = }}\left\{ {{\text{January, March, May, July, August, December}}} \right\}\]

B) \[{\text{A = }}\left\{ {{\text{January, March, May, July, August, October, December}}} \right\}\]

C) \[{\text{A = }}\left\{ {{\text{January,March, April, June, July, August, October,}}}

\right\}\]

D) None of these

Answer
Verified

It is given that; \[A = \{ x/x\] is a month of the Gregorian year having more than \[30\]days}. We have to find it in roster form.

We know that:

Number of days in January is $31$ days.

Number of days in February is $28$ days (in leap year, it will be $29$ days).

Number of days in March is $31$ days.

Number of days in April is $30$ days.

Number of days in May is $31$ days.

Number of days in June is $30$ days.

Number of days in July is $31$ days.

Number of days in August is $31$ days.

Number of days in September is $30$ days.

Number of days in October is $31$ days.

Number of days in November is $30$ days.

Number of days in December is $31$ days.

So, we get the month which is having more than \[30\] days: January, March, May, July, August, October, and December.

\[{\text{A = }}\left\{ {{\text{January, March, May, July, August, October, December}}} \right\}\]

In roster form, all the elements of a set are listed, the elements are being separated by commas and are enclosed within braces {}. It is also known as tabular form.