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Problem 13

Algebra Difficulty 1.0 Prove it CEMC Euclid · Canada · 2026

What is the integer tt for which $2t3+3t2\$\dfrac{2t}{3} + \dfrac{3t}{2} =
26$?
What is the integer xx for which $3+x4=6+x8$\$\dfrac{3+x}{4} = \dfrac{6+x}{8}\$ ?
Suppose that y>0y > 0 and $32+42+122=32+42+y2\$\sqrt{3^2+4^2+12^2} = \sqrt{3^2+4^2} + \sqrt{y^2}.Determinethevalueof. Determine the value of y$.

This one wants a proof. Work it on paper, then read the official solution and mark yourself. Be honest about it: the record is only any use to you if it is.

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Official solution

Multiplying both sides of the equation by 23=62 \cdot 3 = 6, we obtain $6 2t3+63t2\cdot \dfrac{2t}{3} + 6\cdot\dfrac{3t}{2} = 6
\cdot 26or or 4t + 9t =
156$.

Simplifying, we obtain 13t=15613t = 156
and so t=12t = 12.

Alternatively, using a common denominator of 23=62 \cdot 3 = 6, we obtain 2\text{2} 2t}{2 \cdot 3} + 3\text{3}
3t}{3 \cdot 2} = 26or or 4t6+9t6\dfrac{4t}{6} + \dfrac{9t}{6} = 26$.

Simplifying, we obtain $13t6\$\dfrac{13t}{6} =
26andso and so 13t = 6 \cdot 26$
or t=62=12t = 6 \cdot 2 = 12.
Multiplying both sides of the equation by 88, we obtain 8(3+x)4=6+x\dfrac{8(3+x)}{4} = 6 + x which
simplifies to 2(3+x)=6+x2(3+x) = 6 + x.

Simplifying further, we obtain $6 + 2x = 6 +
xandso and so x = 0$.

Alternatively, splitting each fraction into two pieces, we obtain
$34+x4=68+x8$.\$\dfrac{3}{4} + \dfrac{x}{4} = \dfrac{6}{8} + \dfrac{x}{8}\$.

Since 34=68\dfrac{3}{4} = \dfrac{6}{8},
we obtain $x4=x8\$\dfrac{x}{4} = \dfrac{x}{8}andso and so 8x =
4xor or x = 0$.
Since y>0y > 0, then y2=y\sqrt{y^2} = y.

From the given equation, we obtain $9\$\sqrt{9} +
16 + 144} = 9\sqrt{9} + 16} + y$.

Thus, 169=25+y\sqrt{169} = \sqrt{25} + y or
13=5+y13 = 5 + y and so y=8y = 8.

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.