For this week, we focused on the role of mental computation and computational estimation. Mental computation is computation done all in the head that is without tools such as a calculator or pencil and paper. In fact, research has documented a wide variety of mental computation techniques that children have created on their own and that make sense to them (Fuson, 2003). During tutorial hour, we implement the activity based from Groves which is known as ‘How did you do it?’ ,in this activity, our lecturer, Madam Lam, present an additional question which need to be done using mentally. The responses were variety; some using the mental strategy by adding from the left, counting on, making tens, doubling, and making compatibles. For me, it’s hard to explain. I got the answer by automatically and it’s so mystery. When I look up for this type of mental computation in the internet, it’s been shown that it’s very rare to find this type mental strategy. It’s like when someone hit your knee, your knee will automatically reflects. This phenomena known as automatic reflects. Well I suppose that can be best describing my unique mental strategy. Beside from learning the mental computation, we also learn the estimation skills. In my opinion, estimation is very helpful especially when we need to estimating a very large quantity. For example, we need estimating criteria when we doing research to estimating the population of tourists who visiting Sabah every year or estimating the number of bacteria which living in the microorganism habit when doing the microbiologist area. Learning about estimation gives student their first encounter with an area of mathematics that does not focus on exact answers and yet is natural part of mathematics. Estimation involves a different mindset from the mindset that says only an exact answer will do.