Question

If $x^5+1=7777$ and $y^4-1=9999$ then find the value of $xy$ where both $x$ and $y$ are positive integers

• A. $70$
• B. $60$
• C. $80$
• D. $40$

Answer 1

Answer: (B)

$60$

We have,

$x^5+1=7777$ and $y^4-1=9999$

$\Rightarrow x^5=7777-1$ and $y^4=9999+1$

$\Rightarrow x^5=7776$ and $y^4=10000$

$\Rightarrow x^5=6^5$ and $y^4={10}^4$

$\Rightarrow x=6$ and $y=10$

Hence $xy=6\times 10=60$