Question

ii)
A jet plane covers 4500km in sometime. If the regular
speed is decreased by 150 km/hr, it take one and a
half hours more to complete the journey. Find the
original speed of the jet plane.​

Answer 1

Original speed of the Jet plane was 750 km per hour.

Step-by-step explanation:

If a Jet plane covers distance d km in t time then the speed will be defined by

Speed = $\frac{d}{t}$ km per hour

If jet plane covers 4500 km in t hours then speed will be

Speed =  $\frac{4500}{t}$ km per hour

If the speed is decreased by 150 km per hour then time taken by jet = (t + $\frac{3}{2}$) hours

Then expression for speed becomes as

$\frac{4500}{t}-150$ = $\frac{4500}{t+\frac{3}{2} }$

$\frac{4500}{t}-\frac{4500}{t+1.5}=150$

$\frac{1}{t}-\frac{1}{t+1.5}=\frac{150}{4500}$

$\frac{1}{t}-\frac{1}{t+1.5}=\frac{1}{30}$

$\frac{t+1.5-t}{t(t+1.5)}=\frac{1}{30}$

$\frac{1.5}{t(t+1.5)}=\frac{1}{30}$

t² + 1.5t - 45 = 0

By solving this equation from quadratic formula we get t = 6 hours

Therefore, original speed = $\frac{4500}{6}$

Speed = 750 km per hour

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