On top of a digital weighing scale
are four identical glasses, filled with
water, weighs A grams each. Then,
somehow the poison X was sneaked
into one of them with no change in
color, odor or volume. \ / \ / \ / \ /
\__/ \__/ \__/ \__/
==========================
[4 A + x ]
Using the scale once.Can you find out
which of the glasses is poisoned?