Question

Question content area top
Part 1
Scientists often use a pan balance to measure mass when doing experiments. The equation 9 plus 2 plus 1 equals 11 plus 1 represents when a scientist adds 1 unit of mass to each side of a pan balance. Construct an argument to explain how the scientist knows that the pans are still in balance.
Question content area bottom
Part 1
▼
amount of mass was
▼

▼
so the mass in the pans
▼
and the pans stay in balance.

Answer 1

Answer: The amount of mass was equal, so the mass in the pans increased by the same amount and the pans stay in balance.

Explanation: 9 + 2 = 11. If you add 1 to each side you get 9 + 2 + 1 = 11 + 1, i.e. 12 = 12. Adding the same mass to both pans preserves equality, so the balance stays level.