Question 593787
X    Y
2   3
3   5
4   7
5   9


From the data, X moves in steps of 1 point and Y in steps of 2 points. Therefore, if X is increased by 1, Y is increased by 2. 


=> The figures are in sequence, so we need to determine how to go from X to Y, that is 2 to 3, 3 to 5, 4 to 7, and 5 to 9.
From this, it can be seen that the changes between X and Y are 1, 2, 3, and 4 respectively.


Interpretation; 
from X value of 2 to Y value of 3 = 2+1
from X value of 3 to Y value of 5 = 3+2
from X value of 4 to Y value of 7 = 4+3
from X value of 5 to Y value of 9 = 5+4 ; where these adding numbers are the value of the previous X
(2+prev. X value = 3, 3+prev X value = 5 and so on)


Mathematically, the relationship is Y = Current value of X + Previous value of X
Y = X + (X - 1)
Y = X + X -1
Y = 2X - 1 


Verification:
if X = 2 then Y = 2*2 - 1 = 3
if X = 3 then Y = 2*3 - 1 = 5
if X = 4 then Y = 2*4 - 1 = 7
if X = 5 then Y = 2*5 - 1 = 9