Two numbers X and Y are respectively 20% and 28% less than a third number Z. By what percentage is the number Y less than that of the number X?

A. 8% p.a.
B. 6% p.a.
C. 4% p.a.
D. 5% p.a.
E. None of these
Explanation:
Let the rate of interest be R% p.a.
17400[1 + R/100]2 = 17400 + 1783.50
[1 + R/100]2 = (17400 + 1783.50)/17400
= 1 + 1025/10000 = 1 + 41/400
= 441/400 = [21/20]2
[1 + R/100] = 21/20
R/100 = 1/20
Therefore R = 5