There are two questions which seem the same but the answers are different.

1. A corp had gross business income of $260,000 and dividend income of $100,000 from 25% owned domestic corp. Business deduction is $170,000. What is dividends-received deduction?

The answer explains that the DRD is limited to the 80% of taxable income, so the DRD is 80%*(260000-170000)=72000 ($100,000 dividend income is not included in calculation.)

2. A corp had gross receipts of $390,000, operating expenses of $400,000, and dividend income of $120,000 from 20% owned domestic corp. What is Dividends-received deduction?

Th answer also stated that the DRD is limited to the 80% of taxable income, but the calculation of the taxable income is different from the above, which included the dividend received. So the DRD is 80%*(390000+120000-400000)=88000

Could anyone help to tell me which one is correct?

There is something wrong with question 1, dividends must be added to gross gross receipts in order to calculate DRD questions. 

Becker teaches the general rule, the B Limitation, and the Loser rule(exception)---when it creates an NOL. 

Question 2 is correct.