20 12——20 13 seventh-grade mathematics (9) formative test (chapter 3, one-dimensional linear equation) Zhongshan city, Guangzhou.

1, let the sales unit price be x, and get the equation 20%X=X- 1600, X=2000.

2. Let the original number of group B be y, the equation 2X-8=0.5(Y+8)+9, and the solution is Y= 14.

Three or four hours.

If the hourly efficiency of A is x and the hourly efficiency of B is y, we can get 15X= 12Y, and y = (5/4) x.

The workload of Party A 1 hour is X, and the workload of Party B for 4 hours is 4 * (5/4) x = 5x, so the sum of the workloads of both parties is 6X.

Then the remaining workload is 15X-6X=9X, and the sum of the efficiencies of A and B is X+(5/4) X = (9/4) X.

So the remaining working time is 9x÷ (9/4) x = 4.