According to the known conditions: cocoa powder 4 10g, walnut powder 520g, two kinds of chocolate processed 50 pieces;

Cocoa powder:13g, walnut powder: 4g.

Cocoa powder: 5g, walnut powder: 14g.

Cost: original bill: 1.2 yuan.

A jigsaw puzzle: 2 yuan

The title has been set, and the original X block is made. Then make (50-x) puzzles,

Column inequality:

13x+5(50-x)& lt； =4 10

4x+ 14(50-x)& lt； =520

The solution is:: 18

x= 18， 19，20

2:::::

y= 1.2x+2(50-x)

y= 100-0.8x

For the lowest cost, x should be the largest.

x=20

With 20 processed flavors and 30 puzzles, the cost of this scheme is 84.