In 1 minute, I walk = 1/30
In 1 minute, My brother walk = 1/40
In T minutes, I walk = T*1/30
My brother walk 8 minute before = T + 8
In 1 minute, My brother walk = (T + 8)*1/40
When these two distances are same, then I will catch him.
T*(1/30) = (T + 8)*(1/40)
30*(T + 8) = 40*T
30*T + 240 = 40*T
240 = 10*T
T = 24 minutes
hence, I will catch him in 24 minutes.
Take 5 instead of 8.
My brother walk 5 minute before = T + 5
In 1 minute, My brother walk = (T + 5)*1/40
When these two distances are same, then I will catch him.
T*(1/30) = (T + 5)*(1/40)
30*(T + 5) = 40*T
30*T + 150 = 40*T
150 = 10*T
T = 15 minutes
Hence, I will catch him in 15 minutes.
