At this time, the yield is (530-450+10 )×15450×15×100100 = 945 = 20%; (3 points)

(2) Uncle Zhang's loss amount is: 450×16-(530-450+10 )×15-16×10 = 5690 yuan (2 points).

(Or it can be expressed as: 450× 31-530× (1+2+4+8)-10× (1+2+4+8+16) = 566.

Comments: When answering this question, it is necessary to transform pyramid selling behavior into a mathematical problem, which embodies the transformation thought and application value of mathematics.

Solution:

The expenditure of the first phase is 450× 1 yuan, and the return is10×1+530×1yuan.

The second phase expenditure is 450×2 yuan, and the return is 10× 2+530× 2 yuan.

The expenditure in the third phase is 450×4 yuan, and the return is 10× 4+530× 4 yuan.

The expenditure of the fourth phase is 450×8 yuan, and the return is 10× 8+530× 8 yuan.

The total expenditure is 450× 15 = 6750 yuan.

The total income is10×15+530×15 = 8100 (yuan).

Yield (8100-6750) ÷ 6750 =1350 24750 = 0.2 = 20%.

(3)

The accumulated income in the first to fourth periods is 8 100-6750= 1350 (yuan).

fifth

Expenditure 450× 16 = 7200 (yuan)

Return10×16 =160 (yuan)

So the cumulative loss is 7200-160-1350 = 5690 (yuan).