Fraud investigators inc. operates a fraud detection service. on march 31, 10 customers were billed for detection services totaling $24,000. on october 31, a customer balance of $1,450 from a prior year was determined to be uncollectible and was written off. on december 15, a customer paid an old balance of $790, which had been written off in a prior year. on december 31, $490 of bad debts were estimated and recorded for the year.