Date: 29 December 2020

# Aptitude

A man has 9 friends, 4 boys, and 5 girls. In how many ways can invite them, if there have to be exactly three girls in the invites?

• 320

• 160

• 80

• 200

Ans:160

```He can select three girls in 5C3​ ways = 10 ways He can select boys in [4C0​+4C1​+4C2​+4C3​+4C4​] ways = 16 ways Total number of ways =10×16 =160```

# Technical MCQ

Which of the following is correct?

a) Base class pointer object cannot point to a derived class object

b) Derived class pointer object cannot point to a base class object

c) A derived class cannot have pointer objects

d) A base class cannot have pointer objects

Ans: b

`Explanation:``C++ does not allow a derived class pointer to point a base class pointer whereas a Base class can point to a derived class object. Both base class and derived class can have pointer objects.`

# Coding

Given a non-negative integer n, count all numbers with unique digits, x,

where 0 ≤ x < 10n.

Example:

`Input: 2 ​Output: 91`

`Explanation: ``The answer should be the total numbers in the range of 0 ≤ x < 100, excluding 11,22,33,44,55,66,77,88,99`

## Solution:

`int countNumbersWithUniqueDigits(int n) {        if(n==0)            return 1;        int p=9,sum=9;        n--;        int i=9;        while(n--)        {            p=p*i;           sum+=p;            i--;        }        return sum+1;    }`