Question: A fighter jet covers a certain distance at a speed of 1200 km/h in 5 hours. What speed must it maintain to cover the same distance in 250 minutes?

Solution:
Total distance = Speed × Time
= (1200 × 5) km
= 6000 km

Given time = 250 minutes = (250/60) hours= 25/6 hours

∴ Required speed = Distance/Time
= {6000/(25/6)} km/h
= {6000 × (6/25)} km/h
= (240 × 6) km/h
= 1440 km/h

প্রশ্ন: A ও B সমবেগে একটি নির্দিষ্ট পথ যথাক্রমে b1 এবং (b1 + b2) মিনিটে অতিক্রম করে। A ও B এর গতিবেগের অনুপাত কত?

সমাধান:
ধরি,
পথের দূরত্ব = x মিটার 

∴ A এর গতিবেগ = x/b1
∴ B এর গতিবেগ = x/(b1 + b2) 

প্রশ্নমতে,
A/B = (x/b1)/{x/(b1 + b2)}
⇒ A/B = (x/b1) × {b1 + b2)/x}
⇒ A/B = (b1 + b2)/b1
⇒ A : B = (b1 + b2) : b1

Question: Working 5 hours a day, A can complete a work in 9 days and working 9 hours a day, B can complete the same work in 10 days. Working 6 hours a day, they can jointly complete the work in - 

Solution: 
Working 5 hours a day, for 9 days, A can finish the work in = (5 × 9) = 45 hours
Working 9 hours a day, for 10 days, B can finish the work in = (9 × 10) = 90 hours

both together can do in one hour = 1/45 + 1/90
= (2 + 1)/90
= 3/90
= 1/30

so, it will take them 30 hours to do the work.

hence, working 6 hours a day, they need = 30/6 = 5 days

So they will complete the work in 5 days working 6 hours each day.