1, assuming the original price is 1, the prices of the three supermarkets after price reduction are: 0.8*0.8=0.64, 0.6, 0.7*0.9=0.63 respectively.

So supermarket b is the cheapest.

2. It can be concluded that the common divisor of the sequence is: (n squared +(- 1) N+ 1 power), and the seventh number is 1/50.

3. The last item should be one in 2005*2007, right? Otherwise, you can't ask for it.

From the last item, we can decompose 2005 * 2007 =1/2 * (2005-2007).

So1* 31+3 * 5+5 * 7+...+2005 * 2007.

= 1/2*( 1- 1/3+ 1/3- 1/5+ 1/5- 1/7.。 . . . . 1/2005- 1/2007)

= 1/2*( 1- 1/2007)

= 1003/2007

4 can be solved by three problems:

= 1/3*( 1- 1/2008)

=669/2008

5. The absolute value of a-4 +2-a =4-a+a-2=2.

6. Equal to 2

You can set the three numbers of abc as 1, 1, 1, or-1,-1.

7.A

8.B

9.6650 * 7.6%-4780 * 3.87%-1* 4.8-128 =139438+0.4 million yuan.