A group of mathematics teachers went to a restaurant. They agreed to split the bill equally. When the bill arrived, two of them discovered that they had forgotten their money. The others in the group agreed to make up the difference by paying an extra $1.30 each.
If the total bill was $78, how many teachers were in the group?



Let n be the number of teachers at lunch. Then they should have paid 78/n dollars each, but n - 2 of them ended up paying $1.30 more.

That is,