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Question

If a : b = 3 : 2 and b : c = 4 : 5, then a : b : c = ?

This question was previously asked in
RRB NTPC 2024 Undergraduate CBT 1 Question Paper (29-Aug-2025) (Shift 1)
The correct answer is

6 : 4 : 5

Understanding the Ratio Problem

The question asks us to find the combined ratio \(a : b : c\) given two separate ratios: \(a : b = 3 : 2\) and \(b : c = 4 : 5\). To find the combined ratio, we need to make sure the value representing 'b' is the same in both given ratios.

Combining Ratios Step-by-Step

We are given:

  • Ratio 1: \(a : b = 3 : 2\)
  • Ratio 2: \(b : c = 4 : 5\)

Notice that the term 'b' is common to both ratios. However, in Ratio 1, \(b\) is represented by 2, and in Ratio 2, \(b\) is represented by 4. We need to make these values equal.

  1. Find a Common Value for 'b': The least common multiple (LCM) of 2 and 4 is 4. We want 'b' to be 4 in both ratios.
  2. Adjust Ratio 1: The first ratio is \(a : b = 3 : 2\). To make 'b' equal to 4, we need to multiply both parts of the ratio by 2 (since \(2 \times 2 = 4\)). \( a : b = (3 \times 2) : (2 \times 2) = 6 : 4 \)
  3. Keep Ratio 2: The second ratio is \(b : c = 4 : 5\). The value for 'b' is already 4, so we don't need to change this ratio.
  4. Combine the Ratios: Now we have \(a : b = 6 : 4\) and \(b : c = 4 : 5\). Since 'b' is represented by 4 in both, we can combine them directly into the \(a : b : c\) ratio. \( a : b : c = 6 : 4 : 5 \)

Final Combined Ratio

By adjusting the first ratio so that the value of 'b' matches the second ratio, we successfully combined them. The final combined ratio \(a : b : c\) is \(6 : 4 : 5\).

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Similar Questions

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Important Questions from Ratio and proportion

  1. An amount is divided between two friends in the ratio 4: 7. If the second part is ₹6 more than the first, then the difference in amount between two friends is:
  2. If x : y = 8:3, then \((x - y) : (x + y) = ?\)
  3. If the third proportional of 9 and 60 be x, then what is the value of x?
  4. If 36% of first number is equal to four-sevenths of second number, what is the ratio of first number to the second number?
  5. A, B and C invest a sum in the ratio of 61 : 43 : 90, respectively. If they earned a total profit of ₹2,910 at the end of the year, then what is the difference between share of B and C?
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