When a jug is 1/2 filled with marbles, it weighs 2.6 kg. The jug weighs 4 kg when it is full. Find the weight of the empty jug.

1.2 kg is the correct answer

Subtract 2.6 from 4 to get the weight of 1/2 the marbles:

4-2.6=1.4

Double (or multiply by 2) to get the weight of all the marbles (without the jar):

1.4+1.4=2.8

Subtract 2.8 from 4 to get the weight of the jar:

4-2.8=1.2

The empty jug would weigh 1.2kg.