Estimating using compatible numbers

With experience, you should start to recognise easy multiples and division numbers.

A compatible estimate is an easily recognisable number or sum to use as an estimate

Our friends say we are not compatible but are easily recognised.

Example 1

Estimate the division of $2391div11.9$

Diving $2391$ by $11.9$ is very difficult

but $2400/12$ is very easy

$2400/12=200$

NOTE:

The real answer is $200.92$ so you can see our estimation was very close.

Example 2

Estimate the division of $2095div3$

Diving $2095$ by $3$ is very difficult

but $2100/3$ is very easy

$2100/3=700$

NOTE:

The real answer is $698.33$ so you can see our estimation was very close.

Example 3

Estimate the multiplication of $27times43$

Multiplying $27times43$ is difficult

but $25times40$ is easy

$25times40=1000$

NOTE:

The real answer is $1,161$ which is a little bit higher but $1000$ is a suitable guide.

Example 4

Estimate the division of $55764div825$

Dividing $55764$ by $825$ is very difficult

but $56000/800$ is easy

$(560cancel0cancel0)/(8cancel0cancel0)=70$

NOTE:

The real answer is $67.59$ and so $70$ is an apt estimate.