The counting numbers are listed in an array of six columns l

The counting numbers are listed in an array of six columns, labeled A through F, so that the rows alternate between counting from left to right and right to left. If this pattern continues, what number would be the 40th entry in column C?

·A | B | C | D | E | F 12 1097 13 141516 17 18 24 2322 21 20 19 25 26 27 28 29 30

Solution

Pattern: 1st row L--R 1---6

2nd Row R----L 7---12

3rd Row L----R 13----18

4rth R----L 19 ------24

Difference between first entiries of any two rows = 6 f and starts from R----L

So, elements of 40th row would be : 40 , 41 , 42 , 43 , 44 ,45 corresponding to A B C D E F

So, Cth element of 40 th row would be: 42

So, 1 , 7, 13 , 19---

By A.P. an = a1+(n-1)d = 1+ 6d

a40 = 1+ 6*40 = 241

Firts element of 40 the row would be 40