Skill: Estimate quantities using benchmarks

When you estimate, you find an amount that is close to the actual quantity without counting every item. Use a familiar benchmark, such as a group of $10$, and decide which nearby amount is reasonable. Different estimates can be close and still be correct.

Example: A tray has about $86$ beads. Estimate the number of beads.

1. Use groups of $10$ as a benchmark. Nearby groups of $10$ are $80$ and $90$.
2. Compare $86$ with these benchmarks:
   • $86$ is $6$ more than $80$.
   • $86$ is $4$ less than $90$.
3. Since $86$ is closer to $90$, estimate the number of beads as

$$\boxed{\text{about }90\text{ beads}}$$

The exact number is not needed for an estimate. An answer such as about $90$ is reasonable because $86$ is close to $90$.