Question

how do u estimate decimal 

like 11.6 and 0.25

Answer 1

If the number is 0-4 round it down to number that comes before.If the number is 5-9 round it up to the number that comes after.

Answer 2

Estimation is about rounding answers to the nearest whole or to a simple fraction.
11.6 is closer to 12 than it is to 11 so we can estimate that
11.6≈12

And .25 is closer to 0 than it is to .5 so we can estimate
.25≈0

It also depends what place we are rounding to, we can say that .25 is close to .3 because we don't want to have a 0 value
.25≈.3