Add each of the following and check by reversing the order of addends: `1+2+3+4+1996+1997+1998+1999` `10+11+12+13+14+15+16+17+18+19+20`

20,20, 19, 16, 17, 13, 14, 11 ?, ?

Calculate the mode of the following data : 17, 10, 12, 11, 10, 15, 11,14, 11, 12, 13, 11

Find the range of the data : 14, 15, 16, 18, 19, 25, 30, 41, 26, 16, 13, 18, 20 and 26.

Arrange the following ratios in ascending order: 15:14, 8:12, 7:10 & 16:18

The distance (in km) of 40 engineers from their residence to their place of work were found as follows: 5 3 10 20 25 11 13 7 12 31 19 10 12 17 18 11 32 17 16 2 7 9 7 8 3 5 12 15 18 3 12 14 2 9 6 15 15 7 6 12 What is the empirical probability that an engineer lives: within 1/2 km from her place of work?