Tan's electricity bill for the month of August was $267.00. His September bill showed a 2% increase from his August bill. In October, his bill deacreased by 8% from the amount he was billed in August. How much did Tan spend on electricity over the three-month period?

Start by getting what a 1% depression would be:

267,000 / 100 = 2,670 (this is 1%)

In September, his cost increases 2%:

267,000 + 2 * 2,670 = 272,340

In October, the cost decreased by 8%:

267,000 - 8 * 2,670 = 245640

Add the three months up:

267,000 + 272,340 + 245,640 = $784,980