Estimating calculations 2 - 8th Sep 2008

We started the lesson today by trying to recall the first few prime numbers that we discuss a couple of lessons ago.

We then reminded ourselves of the work we were doing last lesson on estimation of answers to calculations. We talked about how dividing by a number less than 1 gives an answer that is bigger than the number we started with.

Dividing by a number less than 1 is the same as multipling by its reciprocal.

For example: to find the answer to . We must remember that 0.1 is the same as and so the reciprocal of 0.1 is 10.

So = 75 x 10 = 750

We identified some more equivalent fraction and decimal that we need to remember:

0.1 = (reciprocal = 10)

0.2 = (reciprocal = 4)

0.125 = (reciprocal = 8 )