# ST Microelectronics Papers: Sample Questions 1 - 3 of 40

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## Question number: 1

### Write in Short

What are the gates used in half adder.

### Explanation

• Two gates are used in half adder digital circuit, namely XOR and AND gate.
• There are two inputs and two outputs to half adder circuit.
• Input: A and B any digital data
• Output: Sum (S) and Carry (C) of input digits A and B
• XOR gate is used to carry out the sum of two input digits and AND gate is used to calculate the carry if present.
• Truth table of half adder circuit:
 A B Sum Carry 0 0 0 0 0 1 1 0 1 0 1 0 1 1 0 1

## Question number: 2

### Write in Short

The girl’s age is twice that of boy, if the boy is four years old. After four years what will be the age of girl?

### Explanation

At present,

Boy’s age, b = 4 years

Girl’s age, g = 2b = 8 years

After 4 years

Boy’s age, = b + 4 = 8 years

Girl’s age, = g + 4 = 12 years

After 4 years age of girl will be 12 years.

## Question number: 3

### Write in Short

Y catches 5 times more fishes than X. If total number of fishes caught by X and Y is 42, then number of fishes caught by X?

### Explanation

Here, Y catches 5 times more fishes than X. So, Y = 5X

And total number of fishes caught by X and Y is 42. So, X + Y = 42

Substituting the value of Y in terms of X

We can get, X + 5X = 42

6X = 42

X = 7