4 minutes
Set up 2 equations and solve
let b represent time taken to ride around block and
let n represent time taken to ride around neighbourhood, then
10b + n = 24 → (1)
5b + 2n = 18 → (2)
multiply (1) by - 2
- 20b - 2n = - 48 → (3)
add (2) and (3) term by term to eliminate n
- 15b = - 30 ( divide both sides by - 15 )
b = 2
substitute b = 2 into (1) and solve for n
20 + n = 24 ( subtract 20 from both sides )
n = 4
Thus it takes 4 minutes to ride around the neighbourhood