Add up each number in parentheses to get 1/4.

The result is: (1/2+1/6+1/2+1/20+...+1/72) ×1/.

Can you count what is in brackets? 1/2= 1 – 1/2, 1/6= 1/2 – 1/3, 1/ 12= 1/3 – / 1/4,……

Original formula = (1/2+1/6+1/2+1/20+...+1/72) ×1/.

=( 1 – 1/2 + 1/2 – 1/3 + 1/3 – ……- 1/8 + 1/8- 1/9) × 1/4 × 128

=8/9 × 32

=256/9

2.

Simplification: 3.5:0.5x= 1.4: 1.6

(Because it is a primary school step, it can only be written as:) 3.5 * 2: 0.5x * 2 =1.4 * 5:1.6 * 5.

7:x=7:8

x=8

I'll add it later

3. Original formula =11*1* 2/2 * 2 * 3/3 * 3 * 3 ... 7/7 * 7 * 8 * 8.

= 1*2+2*3+3*4+4*5+5*6+6*7+7*8

=2+6+ 12+20+30+42+56

= 168

4. Dismantle: 3? /3? - 1+5? /5? - 1+......20 13? /20 13? - 1

= 1- 1+ 1- 1+ 1- 1.......+ 1- 1+ 1- 1

=0

4. (You can just write the following words. ) Observing the above figure, we can find that the length of the three rectangles is 1 and the width is 2. The shadow part of the first rectangle can be added to the shadow part of the second rectangle, and then the shadow parts of the first two rectangles can be added to the third rectangle to form a complete small rectangle with shadows.

So: length * width = 1*2=2.