Olympiad Maths Prep

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Problem 1274

National olympiad, first round
Algebra Difficulty 6.5 Find the answer

Phillip and Paula both pick a rational number, and they notice that Phillip's number is greater than Paula's number by 1212. They each square their numbers to get a new number, and see that the sum of these new numbers is half of 169169. Finally, they each square their new numbers and note that Phillip's latest number is now greater than Paula's by 50705070. What was the sum of their original numbers?

(A) 4(B) 3(C) 1(D) 2(E) 5\text{(A) }-4\qquad\text{(B) }-3\qquad\text{(C) }1\qquad\text{(D) }2\qquad\text{(E) }5

Official solution

1. Let Phillip's number be a a and Paula's number be b b . According to the problem, Phillip's number is greater than Paula's number by 12. Therefore, we can write:
a=b+12 a = b + 12

2. They each square their numbers and the sum of these new numbers is half of 169. Therefore:
a2+b2=1692 a^2 + b^2 = \frac{169}{2}

3. Substitute a=b+12 a = b + 12 into the equation:
(b+12)2+b2=1692 (b + 12)^2 + b^2 = \frac{169}{2}

4. Expand and simplify the equation:
(b2+24b+144)+b2=1692 (b^2 + 24b + 144) + b^2 = \frac{169}{2}
2b2+24b+144=1692 2b^2 + 24b + 144 = \frac{169}{2}

5. Multiply through by 2 to clear the fraction:
4b2+48b+288=169 4b^2 + 48b + 288 = 169

6. Rearrange the equation to standard quadratic form:
4b2+48b+119=0 4b^2 + 48b + 119 = 0

7. Factor the quadratic equation:
(2b+7)(2b+17)=0 (2b + 7)(2b + 17) = 0

8. Solve for b b :
2b+7=0or2b+17=0 2b + 7 = 0 \quad \text{or} \quad 2b + 17 = 0
b=3.5orb=8.5 b = -3.5 \quad \text{or} \quad b = -8.5

9. Since a=b+12 a = b + 12 , calculate a a for each b b :
- If b=3.5 b = -3.5 :
a=3.5+12=8.5 a = -3.5 + 12 = 8.5
- If b=8.5 b = -8.5 :
a=8.5+12=3.5 a = -8.5 + 12 = 3.5

10. Verify which pair satisfies the condition that Phillip's latest number is greater than Paula's by 5070 when squared again:
- For b=3.5 b = -3.5 and a=8.5 a = 8.5 :
a4=(8.5)4=5220.0625 a^4 = (8.5)^4 = 5220.0625
b4=(3.5)4=150.0625 b^4 = (-3.5)^4 = 150.0625
a4b4=5220.0625150.0625=5070 a^4 - b^4 = 5220.0625 - 150.0625 = 5070
- For b=8.5 b = -8.5 and a=3.5 a = 3.5 :
a4=(3.5)4=150.0625 a^4 = (3.5)^4 = 150.0625
b4=(8.5)4=5220.0625 b^4 = (-8.5)^4 = 5220.0625
b4a4=5220.0625150.0625=5070 b^4 - a^4 = 5220.0625 - 150.0625 = 5070

Since both pairs satisfy the condition, we can use either pair. The sum of their original numbers is:
a+b=8.5+(3.5)=5 a + b = 8.5 + (-3.5) = 5

The final answer is 5\boxed{5}

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.