Let the distance that Bob walks east in 10 minutes = x
So.....he is x meters from the intersection in 10 minutes
And Alex is x meters from the intersection after 10 minutes
So....the distance that Alex walks in 10 minutes must be (1200 - x)
So.....in 100 minutes, Bob must be 10x meters east of the intersection
And Alex must be the same distance north of the intersection
So....in 100 minutes Alex walks 10(1200-x) meters......and this distance must equal the 1200 meters to the intersection plus the 10x meters north of the intersection
So
10 (1200 - x) = 10x + 1200 simplify
12000 - 10x = 10x + 1200
10800 = 20x divide by 20
540 = x
So...the distance that Alex is from the intersection after 100 minutes is
Total distance walked - 1200 m
10 (1200 - x) - 1200 =
10(1200 -540) - 1200 = 10(660) - 1200 = 6600 - 1200 = 5400 m
Note that Bob is the same distance from the intersection = 10x = 10(540) = 5400 m
