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Question : The cube of the sum of two given numbers is 1728, while the product of the two given numbers is 32. Find the positive difference between the cubes of the two given numbers.

Option 1: 448

Option 2: 576

Option 3: 480

Option 4: 512


Team Careers360 6th Jan, 2024
Answer (1)
Team Careers360 19th Jan, 2024

Correct Answer: 448


Solution : Let the two numbers be $a$ and $b$
$(a+b)^{3}=1728$
⇒ $a+b=\sqrt[3]{1728}=12$............I
$ab=32$ given,
Now,
$(a+b)^2-(a-b)^2=4ab$
⇒ $(a-b)^2 = 12^2-4\times 32$
⇒ $(a-b)^2 = 16$
⇒ $a-b=4$.................II
By adding eq. I and eq. II
$2a=16$
⇒ $a=8$
Put $a=8$ in eq. I
⇒ $8 +b =12$
⇒ $b=4$
So from this, we know the numbers are $8$ and $4$.
The positive difference between the cubes of these numbers $=(8^{3}-4^{3})=512-64=448$
Hence, the correct answer is 448.

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