Uma was not able to understand the concept of odd and even numbers. In order to improve her understanding, the teacher took some $20$ pebbles of different colours and asked her to pair them up and sort out the numbers from $1$ to $20$ for which pebbles get paired up or do not get paired up:

To introduce subtraction of two-digit numbers in Class III, a teacher proceeded in the following steps:
Step I: Revision of two-digit numbers with understanding of place value system.
Step II:  Use of tally marks to show that smaller number can be subtracted from larger number.
Step III:  Application of subtraction on numbers under each column of place value.

In this case, teacher is developing the lesson:

A teacher introduced multiplication in her class as repeated addition and then by grouping of same number of objects taken multiple times she introduced the 'x' symbol and further conducted a small activity of finding product using criss-cross lines or matchsticks. Here, the teacher is:

When teaching the addition of fractions, a teacher came across the following error.  $\frac{1}{2}+\frac{1}{3}=\frac{2}{5}$ what remedy action can the teacher take in such situation?