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A bus covers the 240 km between two towns in Karnataka. On the return trip the driver averaged 20 km/h more and arrived 1 hour earlier. What was the average speed on the outward trip?

Class 10Quadratic EquationsAlgebra — Quadratics
  • A80 km/h
  • B60 km/h
  • C48 km/h
  • D−80 km/h

Step-by-Step Solution

Let the outward speed be km/h. Outward time , return time , and the return is 1 hour shorter: → → → → → (reject −80). Check: 240/60 = 4 h and 240/80 = 3 h. Answer 80 km/h is the RETURN speed; −80 km/h keeps the rejected root; 48 km/h does not fit.
Answer: B) 60 km/h

Key idea: Word problems with quadratics

Many real-world problems lead to quadratics:

**Number problems**: 'Find two consecutive integers whose product is 132.' Let ; → → or −12. Both valid (or pick positive).

**Area problems**: 'A garden's length is 5 m more than its width. Area is . Find dimensions.'
Let width = . Length = → → (rejecting negative).

**Speed/time/distance**: 'A train takes 1 hour less if its speed is increased by 10 km/h. Original speed?' → typical setup: time1 − time2 = 1 → distance/speed equations → quadratic in speed.

**Always**: reject negative or extraneous roots if context demands positive (lengths, ages, speeds).

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