SITUATION:

Ali read 9 pages of a story book on Monday. On Tuesday, he read a few pages more. The total of pages he has read is 20 pages. 

Number of pages Ali read on Tuesday is unknown.

SOLUTION:

Monday: 9 pages

Tuesday: \(x\) pages (unknown)

Total pages: 20 pages

If we change to mathematic equation, we will get \(9 + x = 20\).

To find \(x\), we will subtract 9 from both parts of the equation.

 \(9 \color{red}- \color{red}9 +x = 20 \color{red}- \color{red}9\)

\(x = 11\)

Therefore, \(x\) is 11.

SITUATION:

Ali collects stamps. He gives 12 stamps to his brother. Ali now has 38 stamps.

Number of stamps Ali collects is unknown.

SOLUTION:

Stamps that Ali collect : \(y\) pieces

Stamps that Ali give to his brother: 12 pieces

Remainder of stamps that Ali have: 38 pieces

If we change to mathematic equation, we will get \(y - 12 = 38\).

To get \(y\), we will add 12 to both sides of the equation.

\(y -12 \color{red}+\color{red}1\color{red}2 = 38 \color{red}+\color{red}1\color{red}2\)

\(y = 50\)

Therefore, \(y\) is 50.