Find a close estimate for: √18

The square root for 18 is 4.242 ..., not sure how you want it estimated

Another way to estimate sqrt (18) is to understand that

sqrt (18)

=sqrt (9) sqrt (2)

=3sqrt (2)

=3*1.414

=4.242

Note: estimate for sqrt (2) can be by common usage, or the fact that 14*14=196.

memorizing a few square-roots is an advantage in these situations:

sqrt (2) = 1.41421356

sqrt (3) = 1.7320508

sqrt (5) = 2.2360680

etc.