Holly finds that (11m - 13n + 6mn) - (10m - 7n + 3mn) = m - 20n + 9mn. What error did Holly make?

Solution:

Holy calculated (11m - 13n + 6mn) - (10m - 7n + 3mn) = m - 20n + 9mn.

The mistake Holly made is that he didn’t solve the brackets first. He only used the additive inverse of 10m when combining like terms.

The correct solution is (11m - 13n + 6mn) - (10m - 7n + 3mn) = m - 6n + 3mn

Holly finds that (11m - 13n + 6mn) - (10m - 7n + 3mn) = m - 20n + 9mn. What error did Holly make?

Summary:

Holly didn’t use additive inverse for all the terms while combining like terms.