26 + 37 = 63. Choice (3)

Solution. Only 0, 1, 6, 8 and 9 make sense, when seen upside down. From these numbers we find that Arvind's bike 1906 => 9061 – 1906 = 7155. Choice (2)

Consider the square root of 1000. The largest prime less than this is 31. So the set of all prime numbers less than or equal to 31 i.e., { 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31} must be represented in set A.

The above set itself cannot be set A, as the members of set A are non-prime.

Therefore, each member of set A must represent exactly one of these prime numbers as, set A is such that maximum number of elements. If, any member of the set is a combination of 2 or more primes from the above set, then the number of elements in set A will get reduced as the members of this set should be co-prime to each other.

Set A could be  {22, 32, 52, 112, 132, 172, 192, 232, 292, 312,}

It can be noted that there are more possibilities for set A. A number of set A could t, a product of exactly one prime number from the original set and another prime number which is not from the original set.

If  none of the prime numbers is used on more than one occasion then the set of numbers will be co-primes and hence satisfy the coordination for set A.

Consider 999

    999 – 99 x 11 = 27 x 37 = 33 x 37

    The prime number 3 from the original set is represented only once even though it is multiplied three times.

    ∴ 999 can be a member of the set and it is obviously the larges

We get a = 4, c = 2, e = 6; b = c + a = 6 + 4 = 10 and b – d = d is given by 10 – 5 = 5.