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Question

In a box, the ratio of number of green stones to black stones is 5 ∶ 8. If there are 24 black stones, then how many total stones are in the box?

The correct answer is

39

Understanding the Ratio of Stones

This problem asks us to find the total number of stones in a box, given the ratio of green stones to black stones and the actual count of black stones. The key concept here is understanding and applying ratios to find unknown quantities.

Analyzing the Given Information

  • Ratio of green stones to black stones = 5 : 8
  • Number of black stones = 24

We need to find the total number of stones in the box.

Solving the Ratio Problem Step-by-Step

The ratio 5 : 8 means that for every 5 green stones, there are 8 black stones. We can represent the number of green stones as a multiple of 5 and the number of black stones as the same multiple of 8. Let this common multiple be \(x\).

  • Number of green stones = \(5x\)
  • Number of black stones = \(8x\)

We are given that the actual number of black stones is 24. So, we can set up an equation:

\(8x = 24\)

Now, we need to solve for \(x\) to find the value of the common multiple:

\(x = \frac{24}{8}\)

\(x = 3\)

Now that we know the value of \(x\), we can find the actual number of green stones:

Number of green stones = \(5x = 5 \times 3 = 15\)

So, there are 15 green stones in the box.

The problem asks for the total number of stones. The total number of stones is the sum of the number of green stones and the number of black stones.

Total stones = Number of green stones + Number of black stones

Total stones = \(15 + 24\)

Total stones = \(39\)

Summary of Calculation

Item Ratio Part Calculation Number of Stones
Green Stones 5 \(5 \times 3\) 15
Black Stones 8 \(8 \times 3\) (Given 24, solved for \(x=3\)) 24
Total Stones \(5+8=13\) \(15 + 24\) 39

Thus, the total number of stones in the box is 39.

Revision Table: Ratio of Stones

Concept Description Application in Problem
Ratio A comparison of two quantities. Written as \(a:b\) or \(\frac{a}{b}\). Given as 5:8 for green to black stones.
Proportion An equation stating that two ratios are equal. Used to find the value of the ratio unit (\(x\)). \(\frac{\text{Green}}{\text{Black}} = \frac{5}{8}\). If Black is 24, Green is found via proportion.
Finding Unknowns Using given information to find missing values in a ratio or proportion. We used the number of black stones (24) and the ratio (8 part) to find the value of one ratio unit, then calculated green stones (5 parts).
Total Quantity The sum of all individual quantities. Calculated by adding the number of green stones and black stones.

Additional Information: Understanding Ratios and Proportions

Ratios and proportions are fundamental concepts in mathematics used to compare quantities and solve problems involving scaling. A ratio like 5:8 tells us the relative size of two groups. It doesn't necessarily mean there are exactly 5 green and 8 black stones, but rather that the number of green stones divided by the number of black stones will always simplify to 5/8.

When we are given the actual number of one part of the ratio, we can use this information to find the actual numbers for all parts. In this problem, knowing that 24 black stones correspond to the '8' part of the ratio allowed us to figure out that each 'unit' of the ratio represents 3 stones (\(24 \div 8 = 3\)). Once we know this unit value (often called the constant of proportionality or represented by \(x\)), we can multiply it by the other parts of the ratio to find their actual quantities.

  • If the ratio is \(a:b\), the quantities can be written as \(ax\) and \(bx\).
  • If the actual value of \(bx\) is given, we can solve for \(x\).
  • Then, we can find the actual value of \(ax\).
  • The total quantity is \(ax + bx\).

This method is widely applicable in various problems involving scaling, mixing, sharing amounts in a given ratio, and converting units.

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Important Questions from Ratio and Proportion

  1. If the ratio of three numbers A, B and C is 2 ∶ 3 ∶ 5, and the sum of the squares of these numbers is 3800, then the value of C is:

  2. A bag contains ₹310 in the form of 5 rupee, 2 rupee and 1 rupee coins in the ratio 4 ∶ 3 ∶ 5. What is the number of 5 rupee coins? 

  3. The ratio of three numbers is 3 ∶ 5 ∶ 4 and the sum of their squares is 11250. Find the sum of the numbers.

  4. When 'x' is subtracted from each of the numbers 22, 39, 56 and 107, then the resulting numbers, in this order, are in proportion. What is the mean proportional between (x + 3) and (3x - 7)?

  5. The salaries of Ravi and Sumit are in the ratio 4 ∶ 5. If the salary of each is increased by Rs. 6,000 the new ratio becomes 35 ∶ 40. What will be Sumit's increased salary?

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