Question Details

The sum of the cubes of two given natural numbers is 9728, while the sum of the two given numbers is 32. What is the positive difference between the cubes of the two given numbers?

Options

A

6272

B

5832

C

4662

D

7904

Show Answer

Correct Answer :

Option A

6272

6272

Solution :

To find the positive difference between the cubes of the two numbers, we can first determine the numbers themselves by using algebraic identities.

Let the two natural numbers be x and y.

From the problem, we are given two conditions:
1. The sum of the two numbers is 32:

x+y=32
2. The sum of the cubes of the two numbers is 9728:

x3+y3=9728

We can use the algebraic identity for the sum of cubes:

x3+y3=(x+y)((x+y)2-3xy)

Substitute the given values into this identity:

9728=32·(322-3xy)

Divide both sides of the equation by 32:

304=1024-3xy

Rearrange the terms to solve for xy:

3xy=1024-304

3xy=720

xy=240

Now we know that the sum of the two numbers is 32 and their product is 240. We can set up a quadratic equation to find the two numbers:

t2-32t+240=0

Factoring the quadratic equation:

(t-20)(t-12)=0

This gives the roots as:

t=20 or t=12
So, the two natural numbers are x=20 and y=12.

Now, we calculate the cubes of these two numbers:

203=8000

123=1728

Finally, we find the positive difference between the cubes:

8000-1728=6272

The correct answer is 6272.

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