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Question

The rectangle represents a set of calculations that are common across all the given equations. Identify the calculations involved and solve the fourth equation on the same basis:

$7 \blacksquare 4 = 27/4$
$6 \blacksquare 1 = 5$
$4 \blacksquare 3 = 11/3$
$a \blacksquare b = ?$

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
$(ab - 1) / b$

Solving the Algebraic Pattern

The problem presents a series of equations with a symbolic operator '$\blacksquare$'. We need to identify the rule governing this operator based on the given examples and apply it to find the expression for '$a \blacksquare b$'.

Analyzing the Given Equations

The provided equations are:

  • $7 \blacksquare 4 = 27/4$
  • $6 \blacksquare 1 = 5$
  • $4 \blacksquare 3 = 11/3$

Identifying the Operator Rule

Let's assume the operation '$a \blacksquare b$' follows a specific algebraic pattern. We test the pattern $a \blacksquare b = (ab - 1) / b$, derived from the options and verified against the examples.

  • For the first equation, $a=7, b=4$: $(7 \times 4 - 1) / 4 = (28 - 1) / 4 = 27/4$ This matches the given result.
  • For the second equation, $a=6, b=1$: $(6 \times 1 - 1) / 1 = (6 - 1) / 1 = 5/1 = 5$ This also matches the given result.
  • For the third equation, $a=4, b=3$: $(4 \times 3 - 1) / 3 = (12 - 1) / 3 = 11/3$ This matches the given result as well.

Solving for '$a \blacksquare b$'

Since the pattern $a \blacksquare b = (ab - 1) / b$ holds true for all given examples, we can conclude this is the correct rule for the operator.

Therefore, for '$a \blacksquare b$', the expression is:

$a \blacksquare b = \frac{ab - 1}{b}$
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Important Questions from Problem Solving

  1. Evaluate 5793405 x 99999

  2. A tight fitting band is wrapped around the Equator. Another circular band whose length is 15 m more lies at a certain height over the first band. A group of human beings attempt to pass under the longer band. Can they walk under it?

    (Earth’s circumference is roughly 40000 km. The height of human beings is between 1 & 2m)

  3. Select the set in which the numbers are related in the same way as are the numbers of the following sets.

    (NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 - Operations on 13 such as adding/subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

    (84, 73, 157) (96, 88, 184)

  4. Arrange the problem-solving strategy.
    (A) Generate many possible solutions
    (B) Determine how to implement the solution and evaluate the success of the solution
    (C) Make a decision
    (D) Evaluate each solution
    (E) Define the problem
    Choose the correct answer from the options given below.
  5. People who are closest to information technology agree with the observation that benefits of screens as a learning tool are overblown and the risks for addiction and stunting development seems high. Screens are said to be beyond personal control and we situate them in pleasure centres of the developing brains. As a responsible parent you will

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