Unit 9
Speed and Time Calculation
About this unit
Tackle multi-step time problems involving international travel, time zone conversions, layover times, relative speed, and scheduling windows. Questions present realistic scenarios requiring careful arithmetic with hours, minutes, and time zone offsets.
What types of questions will you face?
- 1Calculate departure or arrival time for a flight involving time zone differences and known flight duration
- 2Multi-leg flight: add flight time + layover, then apply time zone offset to find local arrival time
- 3Find when two people in different time zones can both be free at the same time
- 4Relative speed: an express train travels N times as fast as a slow train — find its departure time
- 5Multi-stage journey (walk + bus + train): calculate the latest possible departure time to arrive by a deadline
- 6Clock angle calculation: find the angle between clock hands at a given time
Skills you will build
- Converting between time zones by adding or subtracting the offset correctly
- Tracking time across day boundaries (e.g. departing at 11:30 PM Thursday, arriving Friday)
- Adding and subtracting hours and minutes accurately
- Using relative speed relationships (twice as fast = half the time)
- Working backwards from a deadline to calculate the latest valid start time
By the end of this unit, you will be able to
- Solve any multi-leg international flight problem with time zone changes
- Find valid meeting windows for people in different time zones
- Calculate the minimum time needed for a multi-stage journey
- Handle relative speed problems with confidence using the speed-time relationship
Difficulty profile
Medium difficulty (avg 3.00). Single time-zone problems are Easy; multi-leg flights crossing multiple time zones are Difficult. The clock angle question is an unusual harder variant.
Exam tip: Speed and Time Calculation
Draw a timeline. Write departure time, add flight duration, then apply the time zone offset at the end. Always note whether the destination is ahead (+) or behind (-) the origin, and watch for midnight crossings.
Sample Questions
Speed and time are inverses on the same route: travel four times as fast and the journey takes one-quarter as long. Nail that before touching the clock.
Relative-speed timetable questions appear regularly on Selective TS — often as an early item when you translate a speed ratio into minutes on the clock.
The examiner checks whether you can find one vehicle’s trip time, scale it by the speed ratio, then count backwards from a fixed arrival to get the correct departure.
A slow service takes a known time; a faster service uses the same route at a stated multiple of speed. Both must arrive by the same deadline — find when the slower (or faster) one must leave.
Best approach: Step 1: work out the faster train’s elapsed time. Step 2: apply the ratio (4× speed → ÷4 time, etc.). Step 3: subtract from the arrival time. Draw a timeline if AM/PM is tricky.
Question
A slow train leaves Millfield at 7:00 am and reaches Braxton at 1:00 pm the same day. An express train uses the same route at four times the average speed of the slow train. On another day the express leaves Millfield later but still arrives in Braxton at 1:00 pm.
Both trains run at constant speed without stopping.
At what time did the express train leave Millfield?
- A10:00 am
- B11:00 am
- C11:30 am
- D12:00 pm
Decided on your answer? Check how you went below.
Harder time questions stack flight legs, layovers, and a time-zone shift — work in one zone first, convert only at the end.
Multi-leg flight + time-zone items sit in the harder band of Selective mocks; the km distance is usually a red herring when durations are already given.
You must add every flying and waiting segment, find landing time in the departure city’s zone, then apply the offset (ahead = add hours when converting forward, behind = subtract).
A traveller flies via a hub with stated leg times and layover. You are told how cities relate in time zones and asked for local clock time at destination.
Best approach: Ignore distance. Total hours = leg₁ + layover + leg₂. Add to departure local time. Then shift to destination zone once. Never mix zones mid-sum.
Question
Ravi is flying home from Nairobi to Tokyo. Tokyo is 6 hours ahead of Nairobi.
His return journey has two legs:
- Flight from Nairobi to Mumbai: 5 hours
- Layover in Mumbai: 2 hours
- Flight from Mumbai to Tokyo: 9 hours
Ravi boards his first flight in Nairobi at 8:00 AM Friday (Nairobi local time).
What day and time does he land in Tokyo?
What day and time does he land in Tokyo?
- A2:00 PM Friday.
- B6:00 AM Saturday.
- C12:00 AM Saturday (midnight).
- D4:00 AM Saturday.
Decided on your answer? Check how you went below.
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