CAT LRDI Routes & Networks: Concepts, Strategies and Solving Approach

CAT LRDI Routes & Networks questions test your ability to interpret connections, follow possible paths and identify relationships between different points. These questions can seem confusing when you are not clear about how to represent the given information or decide which route to evaluate first. Learning the core concepts and applying a step-by-step solving approach can make these questions easier to handle.

Physics Wallah supports CAT preparation with resources such as concept-based lessons, practice questions, mock tests, study material and revision resources to help you prepare for the LRDI section. Along with understanding Routes & Networks, regular practice can help you improve your speed, accuracy and ability to approach different types of LRDI sets.

What Are Routes & Networks Questions in CAT LRDI?

Routes & Networks is a Logical Reasoning topic in which different points, junctions, stations, or locations are connected through routes. You may have to determine possible paths, calculate travel costs, distribute traffic, or identify valid movements based on given conditions.

A Routes & Networks question may involve:

• One-way or two-way routes

• Starting and ending points

• Intermediate junctions or stations

• Travel time or route costs

• Toll charges

• Traffic distribution

• Multiple teams or people moving through a network

• Restrictions on routes or movements

The main task is to understand how the different points are connected and then apply the conditions given in the question.

How to Read a Directed Street Network

A network diagram can represent several streets connecting different locations. When a street is one-way, an arrow indicates the direction in which movement is permitted.

For example, if a route is represented as:

A → B

you can travel from A to B, but you cannot assume that movement from B to A is permitted.

Before solving a question, identify:

• The starting point

• The destination

• Intermediate junctions

• Direction of every route

• Routes that cannot be used because of their direction

Once the network is clear, begin identifying the possible paths between the required points.

How to Identify Possible Routes

Start from the given point and follow every permitted direction. Record each complete path that eventually reaches the destination.

For example:

A → B → D

and

A → C → D

represent two different routes from A to D.

Listing the routes separately makes it easier to calculate their costs and compare them.

Do not include a path simply because the locations are connected visually. The direction of movement must permit the complete route.

How to Calculate Route Costs

Some Routes & Networks questions assign a travel cost to each street. The total cost of a route is obtained by adding the costs of the streets used along that route.

Suppose:

• A → B costs 10

• B → D costs 15

Then the total cost of travelling from A to D through B is:

10 + 15 = 25

If another route is:

• A → C costs 12

• C → D costs 8

its total cost is:

12 + 8 = 20

The second route therefore has a lower total travel cost.

When comparing routes, calculate the complete cost of each route rather than comparing only one street at a time.

How Toll Charges Affect Route Costs

Some network questions introduce toll charges at particular junctions.

The total cost of a route can then be represented as:

Total Route Cost = Street Costs + Applicable Toll Charges

For example, if a route has a base travel cost of 30 and passes through a junction with a toll of 5, its total cost becomes:

30 + 5 = 35

If another route has a base cost of 28 but passes through a junction with a toll of 10, its total cost becomes:

28 + 10 = 38

Therefore, the route with the lower base cost is not necessarily the route with the lower final cost.

Comparing Routes Using Equations

When toll charges are represented by variables, equations can help compare routes.

Suppose two routes have total costs:

Route A = 25 + x

Route B = 30 + y

If both routes must have the same total cost, you can write:

25 + x = 30 + y

This relationship can help determine the required toll values without testing every possible combination.

How Traffic Is Distributed Across Minimum-Cost Routes

Some Routes & Networks questions involve traffic distribution.

When several routes have the same minimum total cost, traffic may be distributed across those routes according to the condition given in the question.

For example, suppose three routes have total costs of:

• Route 1 = 50

• Route 2 = 50

• Route 3 = 60

If travellers always select a minimum-cost route and traffic is distributed equally among the minimum-cost routes, Routes 1 and 2 will share the traffic.

Route 3 will not receive traffic because its total cost is higher.

This means that route cost and traffic distribution must be analysed together.

How to Use Toll Charges to Control Traffic Flow

Toll charges can change the relative cost of different routes.

Suppose a particular route is carrying more traffic than allowed under the conditions of the question. Increasing the toll on that route may make another route equally attractive or cheaper.

A useful approach is:

1. Identify all possible routes.

2. Calculate their base costs.

3. Add the relevant toll charges.

4. Determine which routes have the minimum total cost.

5. Check how traffic is distributed among those routes.

6. Adjust the toll relationships according to the condition given.

This approach helps avoid repeatedly testing random toll combinations.

How to Solve Equal Traffic Distribution Problems

A question may require equal traffic through two or more junctions or streets.

To solve such a problem, first identify which complete routes contribute traffic to each junction.

For example, if:

• Route A uses Junction X.

• Route B uses Junction X.

• Route C uses Junction Y.

• Route D uses Junction Y.

then the traffic through X depends on the traffic assigned to Routes A and B, while the traffic through Y depends on Routes C and D.

This distinction is important because:

Equal traffic through routes ≠ Equal traffic through junctions

Always trace the complete routes before calculating the traffic at a particular junction.

How to Find Toll Charges Through Logical Relationships? 

When several toll combinations are possible, you do not always need to calculate every route for every option.

Instead:

Step 1: Identify the important routes

Focus on routes directly involved in the condition.

Step 2: Write their total costs

Represent the tolls using variables where necessary.

Step 3: Establish the required relationship

For equal-cost routes:

Cost of Route A = Cost of Route B

For a route that must be more expensive:

Cost of Route A > Cost of Route B

Step 4: Eliminate impossible combinations

Use the necessary conditions to remove options that cannot satisfy the required traffic or cost relationship.

Step 5: Verify the remaining possibility

Check the complete network before finalising the answer.

How to Minimise Total Travel Cost 

Some LRDI questions ask you to minimise the overall travel cost while satisfying an additional traffic condition.

• Begin by identifying the route with the lowest base cost.

• Then check whether using that route satisfies every condition.

• If the cheapest route violates a traffic restriction, consider the next feasible route or combination of minimum-cost routes.

For example, if one route has the lowest cost but would cause more than the permitted percentage of traffic to pass through a particular junction, that route cannot be considered independently. Another route may need to share the traffic.

The objective is therefore not simply to find the cheapest route. You must find the lowest-cost arrangement that satisfies all the given conditions.

How to Solve Complex Network Problems Using Tables? 

Some Routes & Networks questions involve multiple teams moving through a network at different times.

In such questions, a table can make the information easier to manage.

A basic table can have:

Fill in locations that are directly established by the question first.

Then use the remaining conditions to determine the possible movements.

This prevents several simultaneous movements from becoming difficult to track mentally.

How to Apply Constraints to Multiple Routes? 

Multiple-route questions may include restrictions such as:

• Two teams cannot use the same street simultaneously.

• A team cannot visit a particular station.

• A particular location must be occupied at a specific time.

• Two movements cannot happen at the same time.

• A team must pass through a particular station.

• A team must return to its starting point.

Treat each condition as a restriction on the possible arrangements.

When one route is confirmed, update the remaining possibilities. A route assigned to one team may eliminate several options for another team.

How to Handle Time-Based Movement Conditions? 

When every street takes a fixed amount of time to cross, the network can be analysed through successive time intervals.

Suppose travelling from A to B takes one time unit.

If a team starts at A at Time 1, it can reach B at Time 2.

If it then travels from B to C, it can reach C at Time 3.

This allows you to create a movement sequence:

Time 1 → Time 2 → Time 3

For more complex questions, record every team's location at each time interval.

Check each movement against:

• Travel time

• Route direction

• Required intermediate stations

• Restrictions on simultaneous movement

• Conditions involving repeated visits

Common Mistakes in CAT LRDI Routes & Networks

CAT LRDI Routes & Networks questions require you to analyse connected paths, follow directional restrictions, compare route costs and interpret traffic conditions.

Ignoring Route Direction

In a one-way network, an arrow determines the permitted direction. Do not automatically assume that movement is possible in both directions.

Missing a Possible Route

Check every branch from the starting point before concluding that you have identified all possible routes.

Including an Invalid Route

A visually connected path may not be valid if one of its streets cannot be travelled in the required direction.

Comparing Only Base Costs

When tolls are present, compare the complete route cost, including applicable toll charges.

Confusing Route Traffic With Junction Traffic

Traffic through a junction depends on every route passing through that junction. Do not treat one route's traffic as the total traffic through the junction.

Making Assumptions Too Early

Do not fix a route before applying all the conditions. A later restriction may eliminate the initial possibility.

Solving Everything Mentally

Long network questions can involve several simultaneous conditions. Use route lists, equations, diagrams, or tables to keep the information organised.

How to Improve Routes & Networks Accuracy?

Regular CAT LRDI practice can help you become more familiar with network diagrams, route calculations, and conditional reasoning.

After every incorrect answer, identify where the mistake occurred. You may have:

• Missed a route direction

• Overlooked a possible path

• Included an invalid route

• Calculated a route cost incorrectly

• Ignored a toll

• Confused traffic through a route with traffic through a junction

• Applied a condition too late

• Made an assumption before checking all possibilities

For broader CAT preparation, practising different LRDI sets can also help you become more comfortable switching between diagrams, tables, equations, and conditional reasoning.

CAT LRDI Routes & Networks questions become easier to manage when the network is broken into smaller relationships. Identify the routes, calculate the relevant costs, track the movement conditions, and eliminate possibilities systematically. PW’s CAT LRDI preparation resources can help you practise these approaches across different Logical Reasoning problems and build greater familiarity with network-based questions.