Date: 29 December 2020

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
```

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.`

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

where 0 ≤ x < 10n.

**Example:**

Input:2Output: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`

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;}