This puzzle looks easy… until you notice one tiny detail.

On the first scale, one full jar weighs 120 g.

On the second scale, one empty jar and one half-full jar weigh 150 g.

Most people rush to compare 120 and 150 directly—and get the wrong answer.

The secret is to separate the weight of the jar from the weight of the liquid.

Let:

• J = weight of the empty jar
• L = weight of the liquid in a full jar

From the first scale:

J + L = 120

From the second scale:

2J + ½L = 150

Substitute L = 120 − J into the second equation:

2J + ½(120 − J) = 150

2J + 60 − ½J = 150

1.5J = 90

J = 60

Answer: The empty jar weighs 60 grams.

Did you solve it before reading the explanation?