1)

There are x type A toys and 2x- 100 type B toys.

Purchase from Party A: y1= [120x+100 (2x-100) ]× 0.7+2200.

y 1=224x-4800

Buy from b:

y2 = 100×(x+2x- 100)×0.8

y2=240x-8000

2)

y 1=y2:

224×4800 = 240×8000

240x-224x=8000-4800

16x=3200

x=200

2x- 100=300

200+300=500

When buying 500 toys, the expenses of the two companies are equal.

3)

y 1 & gt； y2:

224x-4800 >240x-8000

240 x-224 x & lt； 8000-4800

16x & lt； 3200

x & lt200

x+2x- 100 & lt； 500

When the total number of people is less than 500, the cost of A is expensive.

When the total number exceeds 500, the cost of A is cheaper.

So: buy 800 toys, the cost of A is cheap, you should buy A toys.