Sum of square of first number and cube of second number together is 568. Also square of the second number is 15 less than square of 8. What is the value of three-fifth of the first number ?

• A. 7
• B. 9
• C. 6
• D. 8

Answer: (B)

Let the first number be x and the second number be y.∴ y² = 82 - 15 = 64 - 15 = 49∴ y = 7∴ x² + 73 = 568= x² + 343 = 568= x² + 568 - 343 = 225∴ x = √225 = 15∴ 15 x 3/5 = 9