Sneha travels 30 km to her college, partly by bicycle at 10 km/h and partly by bus at 40 km/h, and the whole journey takes 1 hour 30 minutes. How far does she travel by bicycle?

Let her cycle $x$ km and travel $y$ km by bus. $x+y=30$ and $x/10+y/40=1.5$. Multiplying the time equation by 40: $4x+y=60$. Subtracting the first: $3x=30$, so $x=10$ and $y=20$. Check: 10 + 20 = 30 and 1 + 0.5 = 1.5 hours. 20 km is the bus distance, the other unknown; 15 km splits the distance equally; 7.5 km comes from splitting the time equally, giving 45 minutes of cycling at 10 km/h.