A plane left 30 min later than the scheduled time and in order to reach its destination 1500 km away in time, it has to increase its speed by 250km/hr from its usual speed. Find its usual speed?

Asked by Anjana S | 23rd Nov, 2014, 07:00: PM

Expert Answer:

L e t space t h e space u s u a l space s p e e d space o f space t h e space p l a n e space b e space x space k m divided by h r N e w space s p e e d space o f space t h e space p l a n e space equals space left parenthesis x plus 250 right parenthesis space k m divided by h r 1500 over x minus fraction numerator 1500 over denominator left parenthesis x plus 250 right parenthesis end fraction equals 30 over 60 rightwards double arrow fraction numerator 1500 x plus 1500 cross times 250 minus 1500 x over denominator x left parenthesis x plus 250 right parenthesis end fraction equals 1 half rightwards double arrow 1500 cross times 250 cross times 2 equals x left parenthesis x plus 250 right parenthesis rightwards double arrow 750000 equals x squared plus 250 x rightwards double arrow x squared plus 250 x minus 750000 equals 0 rightwards double arrow x squared plus 1000 x minus 750 x minus 750000 equals 0 rightwards double arrow x left parenthesis x plus 1000 right parenthesis minus 750 left parenthesis x plus 1000 right parenthesis equals 0 rightwards double arrow left parenthesis x plus 1000 right parenthesis left parenthesis x minus 750 right parenthesis equals 0 therefore x equals 750 comma space minus 1000 therefore U s u a l space s p e e d space o f space t h e space p l a n e space equals space 750 space k m divided by h r

Answered by Prasenjit Paul | 24th Nov, 2014, 09:27: AM