# 3i Infotech Placement: Sample Questions 876 - 878 of 1245

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## Question 876

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### Describe in Detail

Essay▾

What is Relational Calculus?

### Explanation

• Relational calculus is an query language which is non procedural, and instead of algebra it uses mathematical predicate calculus.
• The relational calculus is not the same like that of differential and integral calculus in mathematics, but takes its name from a branch of symbolic logic termed as predicate calculus.
• When applied to databases, it is found in two forms. These are
• Tuple relational calculus which was originally proposed by Codd in the year 1972 and
• Domain relational calculus which was proposed by Lacroix and Pirotte in the year 1977

## Question 877

Edit

### Describe in Detail

Essay▾

What is a concrete class?

### Explanation

• A concrete class defines useful object that can be instantiated as an automatic variable on the program stack.
• The implementation of a concrete class is defined.
• It is not intended to be a base class.
• Concrete is the default type of class such class can have direct instances.
• A derived class that implements all the missing functionality is the concrete class in inheritance.

## Question 878

### Question

MCQ▾

If a sum of money compound annually amounts of thrice itself in 3 years. In how many years will it become 9 times itself?

Choice (4)

a.

6

b.

10

c.

12

d.

8

a.

### Explanation

A sum of money compound annually amounts of thrice itself in 3 years.

We know that,

Where, A = Amount, P = Principal, R = rate and n = number of years

As per the information,

So,

We are asked to find the number of years in which amount will be 9 times the principal.

Let in n years amount will be 9 times the principal.

So,

From equation (i) ,

So,

So, in 6 years amount will be 9 times the principal sum.

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