The logic follows here is : Cube of first number + cube of (first number - 1) = Second number For 7:559=73+(7−1)3=73+63=343+216=559 1) 11:786=(11)3+(11−1)3=(11)3+(10)3=1331+1000=2331≠786 2) 9:593=93+(9−1)3=93+83=729+512=1241≠593 3) 3:35=33+(3−1)3=33+23=27+8=35 4) 5:89=53+(5−1)3=53+43=125+64=189≠89 Hence, "3 : 35" is the correct answer.