Estimating is designed to be an educated guess either to (a) access prior knowledge or to (b) evaluate the reasonableness of an answer . For each of the following estimation strategies:

  1. Research and describe the strategy.
  2. Create two examples when the estimation strategy is appropriate to use (one easy, one complex).
  3. Create one example where the strategy is not accurate, with explanation.

1. Front-end (+)

For two highest place values only.

2. Clustering (+)

3. Compatible numbers (+, –, ×, ÷)

4. Rounding (+, –, ×, ÷)

Why round up on a 5, but down on a 4?

Mental math

The techniques for mental arithmetic are related to estimation techniques, only the accuracy of the final answer is in question. For each of the following mental math strategies:

  1. Describe the strategy
  2. Explain why the strategy works. Is the strategy similar to estimation strategies or alternate algorithms?
  3. Create and solve two examples using whole numbers (one easy, one complex).

5. Use compatibles (+)

6. Balancing, aka. compensation (+, –)

7. Tack on trailing zeros(+, ×, ÷)

Why doesn't this say "add zeros"?

8. Front-end (+)

All place values.