Question Details

The product of two positive numbers is 616. If the ratio of the difference of their cubes to the cube of their difference is 157:3, then the sum of the two numbers is

Options

A

58

B

50

C

95

D

85

Show Answer

Correct Answer :

Option B

50

Solution :

The correct option is 2 (which corresponds to 50).

Let the two positive numbers be x and y, with x>y>0.

We are given that their product is:
xy=616

We are also given the ratio of the difference of their cubes to the cube of their difference is 157:3:
x3y3(xy)3=1573

Recall the algebraic identities:
x3y3=(xy)(x2+xy+y2)
and
(xy)3=(xy)(xy)2

Substituting these into the ratio equation, we can cancel (xy) since the numbers are positive and distinct (as their ratio involves a non-zero difference):
x2+xy+y2(xy)2=1573

We can rewrite the numerator x2+xy+y2 as (xy)2+3xy:
(xy)2+3xy(xy)2=1573

Dividing the terms on the left side, we get:
1+3xy(xy)2=1573

Subtract 1 from both sides:
3xy(xy)2=1543

Substitute xy=616 into the equation:
3×616(xy)2=1543

Simplify the equation by dividing both sides by 154 (note that 616=4×154):
3×4(xy)2=13

Cross-multiplying gives:
(xy)2=3×4×3=36

Since x>y, we have:
xy=6

We need to find the sum of the two numbers, x+y. We can use the relation:
(x+y)2=(xy)2+4xy

Substitute the values of (xy)2 and xy:
(x+y)2=36+4×616
(x+y)2=36+2464=2500

Taking the positive square root (since x and y are positive):
x+y=50

Thus, the sum of the two numbers is 50.

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