Maths Olympiad Prep

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Algebra Difficulty 2.5 Junior Find the answer Canada

Anna and Yao are 42 km42~\text{km} apart. They jog towards each
other along a straight road. Anna jogs at a constant rate of 6 km/h6~\text{km/h} and Yao jogs at a constant
rate of 8 km/h8~\text{km/h}. When they
meet, how much farther has Yao travelled than Anna?

Pick one

Solution

Solution 1:

Each hour, Anna jogs 6 km6\text{ km}
and Yao jogs 8 km8\text{ km}, and so
combined they jog $6 km+8 km=14\$6\text{ km}+8\text{ km}=14\text{} km}$.

After 22 hours, they combine to jog
2×14 km=28 km2\times14\text{ km}=28\text{ km},
and after 33 hours, they combine to
jog $3×14 km=42\$3\times14\text{ km}=42\text{}
km}$.

Since they started 42 km42\text{ km}
apart, then after 33 hours they
meet. After 33 hours, Anna has
jogged $3 h×6 km/h=18\$3\text{ h}\times 6\text{ km/h}=18\text{} km},Yaohasjogged, Yao has jogged 3 h×8 km/h=243\text{ h}\times8\text{ km/h}=24\text{}
km},andsoYaohastravelled, and so Yao has travelled 24 km18 km=624\text{ km}-18\text{ km}=6\text{} km}$
farther than Anna.

Solution 2:

Anna jogs at 6 km/h6\text{ km/h} and
Yao jogs at 8 km/h8\text{ km/h}, and so
they are moving toward one another at a constant rate of $6 km/h+8 km/h=14\$6\text{ km/h}+8\text{ km/h}=14\text{}
km/h}$.

Thus combined Anna and Yao will travel 42 km42\text{ km}, and meet after 42 km14 km/h=3\dfrac{42\text{ km}}{14\text{ km/h}}=3
hours.

Since Yao jogs $8 km/h6 km/h=2\$8\text{ km/h}-6\text{ km/h}=2\text{} km/h}$ faster than Anna jogs, then Yao travels
$2 km/h×3 h=6\$2\text{ km/h}\times 3\text{ h}=6\text{}
km}$ farther than Anna.

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