Maths
One day in class, I was teaching students in 7th standard how to write the standard form and expanded form of large numbers. As I was walking around the room checking students work, I noticed students making a common mistake. They were writing the commas of the large numbers in the wrong places. I helped the students who I found making the mistake and moved on to the next example. Then, I looked at the book for more example problems to work out and found a whole section where numbers had misplaced commas. Oh, the mistake is in the book! That's why students are making these mistakes, I thought. I walked over to my mentor teacher and pointed out the problem. "There seems to be a typo in the book, ma'am. Look at all these numbers with misplaced commas!" "Oh, no, no, no," she said, chuckling as she shook her head. "This is the Indian system of writing numbers. See, after writing the first three digits, we place the comma. Then, we put a comma after every...