Maths Olympiad Prep

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Algebra Difficulty 5.6 AIME, harder Prove it Philippines

Problem:

The sum of the product and the sum of two integers is 9595. The difference between the product and the sum of these integers is 5959. Find the integers.

Solution

Solution:

Let the two integers be xx and yy.

Let S=x+yS = x + y (sum), P=xyP = x y (product).

We are given:

P+S=95P + S = 95 \quad (1)

PS=59P - S = 59 \quad (2)

Add (1) and (2):

P+S+PS=95+59P + S + P - S = 95 + 59

2P=1542P = 154

P=77P = 77

Now substitute P=77P = 77 into (1):

77+S=9577 + S = 95

S=18S = 18

So x+y=18x + y = 18, xy=77x y = 77.

The integers are the roots of the equation:

t2(x+y)t+xy=0t^2 - (x + y)t + x y = 0

t218t+77=0t^2 - 18 t + 77 = 0

Solve for tt:

t=18±1824×772t = \frac{18 \pm \sqrt{18^2 - 4 \times 77}}{2}

=18±3243082= \frac{18 \pm \sqrt{324 - 308}}{2}

=18±162= \frac{18 \pm \sqrt{16}}{2}

=18±42= \frac{18 \pm 4}{2}

So t=18+42=11t = \frac{18 + 4}{2} = 11 or t=1842=7t = \frac{18 - 4}{2} = 7

Therefore, the integers are 77 and 1111.

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Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.