Brief Overview of Python

Invalid identifier names are:

- a) `Serial_no.` — contains a dot (`.`), which is not allowed.
- b) `1st_Room` — starts with a digit, and an identifier cannot start with a digit.
- **c) `Hundred$`** — contains **`$`, a special symbol not allowed.
- d) `Total Marks` — contains a space, which is not allowed.
- f) `total-Marks` — contains a hyphen (`-`), which is not allowed.
- h) `True` — it is a keyword/reserved word, so it cannot be used as an identifier.

Valid identifiers are e) `Total_Marks` and g) `_Percentage`**.

The required assignment statements are:

```python
length = 10
breadth = 20
```

```python
sum = (length + breadth) / 2
```

```python
stationery = ['Paper', 'Gel Pen', 'Eraser']
```

```python
first = 'Mohandas'
middle = 'Karamchand'
last = 'Gandhi'
```

```python
fullname = first + ' ' + middle + ' ' + last
```

The blank spaces are added using `' '` so the full name is joined properly.

The suitable data types are:

- a) Number of months in a year — int, because it is a whole number.
- b) Resident of Delhi or not — bool, because it has only two values: yes/no, true/false.
- c) Mobile number — str, because it is better treated as a string of digits and may contain leading zeroes.
- d) Pocket money — float, because it may include paise/decimal part.
- e) Volume of a sphere — float, because it may come as a decimal value.
- f) Perimeter of a square — float, because the side length may be fractional, so the result may also be decimal.
- g) Name of the student — str, because it is text.
- h) Address of the student — str, because it is text.

Step by step:

- a) `num1 += num2 + num3` means `num1 = num1 + (num2 + num3)`
- `num2 + num3 = 3 + 2 = 5`
- `num1 = 4 + 5 = 9`

- b) `print(num1)` prints 9.

- c) `num1 = num1 (num2 + num3)`
- `num2 + num3 = 3 + 2 = 5`
- `num1 = 9 5 = 59049` if using the updated value from part (a)

But in such textbook output questions, each part is usually treated separately unless stated otherwise. Since the question says “when num1 = 4, num2 = 3, num3 = 2”, the sequence is interpreted in order. Therefore after (a), `num1` is 9, so:
- `num1 = 9 5 = 59049`

- d) `print(num1)` prints 59049.

- e) `num1 = num2 + c` causes an error because `c` is not defined.

- f) `num1 = '5' + '5'` joins strings, so the result is `'55'`.

- g) `print(num1)` prints 55.

- h) `print(4.00/(2.0+2.0))`
- denominator `2.0 + 2.0 = 4.0`
- `4.00 / 4.0 = 1.0`

- i) `num1 = 2 + 9*((3*12)-8)/10`
- `3*12 = 36`
- `36 - 8 = 28`
- `9 * 28 = 252`
- `252 / 10 = 25.2`
- `2 + 25.2 = 27.2`

So `num1` becomes 27.2.

- j) `print(num1)` prints 27.2.

- k) `num1 = float(10)` converts to 10.0.

- l) `print(num1)` prints 10.0.

- m) `num1 = int('3.14')` gives an error because `'3.14'` is not a valid integer string.

- n) `print(num1)` is not executed because the program has already stopped at the error in (m).

- o) `print(10 != 9 and 20 >= 20)`
- `10 != 9` is True
- `20 >= 20` is True
- `True and True` is True

- p) `print(5 % 10 + 10 < 50 and 29 <= 29)`
- `5 % 10 = 5`
- `5 + 10 = 15`
- `15 < 50` is True
- `29 <= 29` is True
- `True and True` is True

So the outputs/values are as listed above.

- a) `25 / 0` — runtime error, because division by zero cannot be executed.
- b) `num1 = 25; num2 = 0; num1 / num2` — runtime error, because the division by zero occurs during execution.

```python
# Calculate amount payable on simple interest
P = float(input("Enter principal: "))
R = float(input("Enter rate of interest: "))
T = float(input("Enter time in years: "))

SI = (P * R * T) / 100
Amount = P + SI

print("Simple Interest =", SI)
print("Amount payable =", Amount)
```