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Q2·CSAT · Prelims 2026

Optimization — Base Cylinder Compounding

NumericalNumber SystemArithmetic ProblemMedium

Question

What is the minimum number of times one needs to measure to get 298 litres of water from a tank, if the measuring cylinders have capacities 1 litre, 6 litres, 25 litres and 100 litres?

Options

a

4

b

5

c

9

Answer
d

13

Explanation

To minimize the total number of measurements needed to reach exactly 298 liters, apply a standard mathematical greedy approach, selecting the largest possible volumetric measures sequentially.

Step 1 (100L base): Take two 100-liter measures \rightarrow 2 × 100 = 200 liters. Remaining: 298 - 200 = 98 liters. (Total measures so far: 2)
Step 2 (25L base): Take three 25-liter measures \rightarrow 3 × 25 = 75 liters. Remaining: 98 - 75 = 23 liters. (Total measures so far: 2 + 3 = 5)
Step 3 (6L base): Take three 6-liter measures \rightarrow 3 × 6 = 18 liters. Remaining: 23 - 18 = 5 liters. (Total measures so far: 5 + 3 = 8)
Step 4 (1L base): Take five 1-liter measures \rightarrow 5 × 1 = 5 liters. Remaining: 5 - 5 = 0 liters. (Total measures: 8 + 5 = 13)

Let us check if a non-greedy allocation yields fewer steps by overshooting: 3 × 100 = 300 liters. To get back to 298, we would need to remove 2 liters, but since we are drawing water from a tank with standard cylinders, we can only add positive measurements to aggregate the total volume. Alternatively, using four 25L components instead of a 100L container increases our count. Let's look closely at the math for another configuration: 2 × 100 + 4 × 25 = 300 (exceeds). Let's review 2 × 100 + 3 × 25 + 3 × 6 + 5 × 1 = 13. Let's check if we can optimize using 298 = 200 + 100 - 2 (cannot subtract). Is there a combination like 2 × 100 + 3 × 25 + 4 × 6 - 1 × 1 = 13? Let's re-verify the baseline math. If we pick 298 = 2 × 100 + 3 × 25 + 3 × 6 + 5 × 1 = 13 steps. Let's test alternative groupings: 2 × 100 + 4 × 25 = 300 (cannot do). Can we use 298 = 2 × 100 + 3 × 25 + 4 × 6 = 299 (close, but need 1L residual adjustment). The exact step distribution corresponds to 2 + 3 + 3 + 5 = 13.

Minimizing independent structural increments involves checking the coefficients when breaking down a target number across given baseline values.

Answer: (d).

Question details

Year

2026

Paper

CSAT

Question

Q2

Section

Quantitative Aptitude

Sub-topic

Number System

Type

Arithmetic Problem

Difficulty

Medium

Source hint

Standard optimization — greedy breakdown algorithms

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