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Algebra Difficulty 7.0 National olympiad, round 2 Find the answer

Students in the class of Peter practice the addition and multiplication of integer numbers.The teacher writes the numbers from 11 to 99 on nine cards, one for each number, and places them in an ballot box. Pedro draws three cards, and must calculate the sum and the product of the three corresponding numbers. Ana and Julián do the same, emptying the ballot box. Pedro informs the teacher that he has picked three consecutive numbers whose product is 55
times the sum. Ana informs that she has no prime number, but two consecutive and that the product of these three numbers is 44 times the sum of them. What numbers did Julian remove?

A number or a short expression. Spacing and $ signs are ignored.

Solution

Let's analyze the information provided about Pedro and Ana to solve the problem and find out which numbers Julian removed.

### Pedro's Drawn Numbers

We are told that Pedro picks three consecutive numbers whose product is 5 times their sum. Let a a , a+1 a+1 , and a+2 a+2 be the consecutive numbers drawn by Pedro. Therefore, we have:

- Product:
a(a+1)(a+2) a(a+1)(a+2)

- Sum:
a+(a+1)+(a+2)=3a+3=3(a+1) a + (a+1) + (a+2) = 3a + 3 = 3(a + 1)

According to the problem, the product is 5 times the sum:
a(a+1)(a+2)=5×3(a+1) a(a+1)(a+2) = 5 \times 3(a + 1)
Simplifying gives:
a(a+1)(a+2)=15(a+1) a(a+1)(a+2) = 15(a + 1)

Divide both sides by a+1 a+1 (assuming a1 a \neq -1 ):
a(a+2)=15 a(a+2) = 15
a2+2a15=0 a^2 + 2a - 15 = 0

Solving the quadratic equation:
(a3)(a+5)=0 (a-3)(a+5) = 0
Thus, a=3 a = 3 or a=5 a = -5 . The value a=5 a = -5 is not possible as it does not fit the range, therefore Pedro's numbers are:
3,4,5 3, 4, 5 .

### Ana's Drawn Numbers

Ana mentions she picked only non-prime numbers, where two of them are consecutive and the product is 4 times the sum. The non-prime numbers in the range 1 to 9 are 1,4,6,8,9 1, 4, 6, 8, 9 .

Let b,c,d b, c, d be Ana's numbers, such that two are consecutive. We need to test combinations fitting the condition that:
bcd=4(b+c+d) bcd = 4(b+c+d)

By testing combinations, let's choose 4,6 4, 6 as Ana's consecutive non-prime numbers:

Combining with 8:
- Product:
4×6×8=192 4 \times 6 \times 8 = 192

- Sum:
4+6+8=18 4 + 6 + 8 = 18

Verification:
192=4×18=72 192 = 4 \times 18 = 72

It doesn’t satisfy.

Now try combining 4,6,94, 6, 9:
- Product:
4×6×9=216 4 \times 6 \times 9 = 216

- Sum:
4+6+9=19 4 + 6 + 9 = 19

Verification:
216=4×19 216 = 4 \times 19

Thus, Ana’s numbers are 4,6,9 4, 6, 9 .

### Julian's Drawn Numbers

Since Pedro has picked 3,4,5 3, 4, 5 and Ana has picked 4,6,9 4, 6, 9 , the remaining numbers for Julian, drawn from 1 to 9, that have not been picked are:
- Remaining numbers: 1,2,6,7,8 1, 2, 6, 7, 8 .

Since Ana already took 6, 9, and needs two consecutive:
- The consecutive pair 6 and 7 fits for Julian

Let's verify if Julian's numbers can reasonably be drawn:
Therefore, Julian’s numbers are 2,6,7 \boxed{2, 6, 7} .

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