The ratio of three numbers is 4 : 5 : 7 and the sum of their cubes is 4256. Find the ratio of the sum of squares of 1st two numbers to the sum of squares of last two numbers.
Answer
Correct Answer : a ) 41 : 74
Explanation :According to the question:
Ratio of three numbers = 4 : 5 : 7
Let the numbers be 4x, 5x and 7x
(4x)3 + (5x)3 + (7x)3 = 4256
64x3 + 125x3 + 343x3 = 4256
532x3 = 4256
x3 = 4256/ 532
x3 = 8
x = 2
Thus, the numbers are
1st number = 4x = 4 *2 = 8
2nd number = 5x = 5 *2 = 10
3rd number = 7x = 7 * 2 = 14
Therefore, sum of square of 1st two numbers = (8)2 + (10)2 = 64 + 100 = 164
Sum of square of last two numbers = (10)2 + (14)2 = 100 + 196 = 296
Required ratio = 164 : 296
Required ratio = 41 : 74
Hence, (a) is the correct answer.
Comments