iarjelIARJELIARJEL2708-5120https://doi.org/10.47310/iajel.2021.v02i02.030Exploring In-Service Mathematics Teachers’ Knowledge on Whole Number Multiplication Using AlgorithmsDennisOffeiKwakyeExploration of some selected permanent in-service mathematics teachers on the life meaning of multiplying whole numbers using algorithms. This study was a qualitative research method which used an unguided interview as the primary source of data collection and to explore the views of in-service or practicing mathematics teachers on how they teach in the normal classroom setting, the topic, multiplication of whole numbers. In the study, in-service or practicing mathematics teachers’ views were solicited through the interview discussion and it was observed that, almost all the teachers use the Long Multiplication algorithm to teach multiplication of whole numbers. About 25% of the participants recalled using Groupings. The objectives were to find out the multiplication algorithm that in-service or practicing mathematics teachers use in teaching multiplication of whole numbers and review the understanding or the meaning in-service or practicing mathematics teachers make in using the algorithm. Findings shows that, almost 99% of the participants use the Long Multiplication algorithm with 78 and 50% using the Groupings and Repeated Addition respectively. On Area Model Meanwhile, these algorithms make no sense to both teachers in the public and private schools as well as their students. The teachers were introduced to the use Realistic Mathematics Education (RME) approach using the Area Model. It was observed that, none of the participants have ever seen, heard or use it before. Despite the fact that, on the average, each teacher has taught mathematics in the basic school at least 14 years. Further recommendations and suggestions put forward by these teachers included, the organization of workshop, in-service training for the in-service mathematics teachers. It was recommended that Mixed-Methods Explanatory Sequential research design be used for further studies to know the motivation or the interest level of in-service mathematics teachers in the use of Area Model multiplication of whole numbers.