2.

The greatest common factor of 4 and 5 is 1, and the smallest common multiple is 20; The greatest common factor of 6 and 16 is 2 and the least common multiple is 48; the greatest common factor of 15 and 25 is 5 and the least common multiple is 75; The greatest common factor of 2 1 and 63 is 2 1, and the smallest common multiple is 63. ..

3.

This picture is not easy to draw.

4.

2/7 = (6)/219/12 = 3/(4) 5 ÷ 3 = (5)/3 =1and (2)/(3)

5.

0.32 1/2>9/20>2/5

It is found that the share of per capita food expenditure in per capita expenditure is less and less every year, and it is decreasing year by year.