Watch gains 10s in 5 min
$\text{Gain rate} = \dfrac{10}{5} = 2 \text{ s per minute}$
$\text{Every } 60 \text{ s real time} \Rightarrow \text{watch shows } 62 \text{ s}$
Watch time elapsed:
$9:00 \text{ am to } 7:20 \text{ pm} = 10 \text{ hr } 20 \text{ min} = 620 \text{ min}$
Real time formula:
$\text{Real time} = \text{Watch time} \times \dfrac{60}{62}$
It was 9.35 AM in Garvita’s watch, which kept
correct time, when Manya informed her that the last
bus left the bus stop at 9.25 am. Manya’s watch is 5
min fast. The frequency of the bus is every 20 min.
For how long Garvita must wait to catch the next
bus?
Garvita’s time is correct, so current time = 9:35 AM.
Manya’s watch is 5 minutes fast, so 9:25 AM on Manya’s watch means actual time = 9:20 AM.
Buses come every 20 minutes, so next bus after 9:20 AM is at 9:40 AM (actual time).
Waiting time = 9:40 AM − 9:35 AM = 5 minutes.
A doctor said to his compounder "I go to see the patients at their residence after every 3 hours 30
minutes. I have already gone to the patient 1 hour 20 minutes ago and next time I shall go at 1:40
P.M." At what time this information was given to the compounder by the doctor?
A clock is set right at 5 AM. It loses 16 minutes in 24 hours.
In 24 hours of correct time, the faulty clock runs only:
$24 - \frac{16}{60}$ hours $= 24 - \frac{4}{15} = \frac{360-4}{15} = \frac{356}{15}$ hours
So, speed ratio (Faulty : Correct) is:
$\dfrac{\text{Faulty time}}{\text{Correct time}} = \dfrac{24 - \frac{16}{60}}{24} = \dfrac{356/15}{24} = \dfrac{356}{360} = \dfrac{89}{90}$
That is, in the time when correct clock shows 90 hours, faulty clock shows 89 hours.
So,
$89$ hours of faulty clock $= 90$ hours of correct clock.
Now, find how many hours the faulty clock indicates from 5 AM (Day 1) to 10 PM (Day 4):
From 5 AM Day 1 to 5 AM Day 4 $= 3$ days $= 72$ hours
From 5 AM Day 4 to 10 PM Day 4 $= 17$ hours
So total indicated (faulty) time:
$72 + 17 = 89$ hours
Since $89$ faulty hours correspond to $90$ correct hours, the true elapsed time is:
$90$ hours $= 3$ days $+ 18$ hours
Start time was 5 AM (Day 1). After 3 days, it will be 5 AM (Day 4).
Add 18 hours to 5 AM (Day 4):
$5\ \text{AM} + 18\ \text{hours} = 11\ \text{PM}$
Therefore, when the faulty clock indicates 10 PM on the 4th day,
the true time is $11\ \text{PM}$.
Jimmy saw the time while going to the tennis court. He saw the hour hand is 20° away from 4. After
he returned from tennis court, he noticed that the hour hand is 20° away from 4. If he took ten
minutes to go to tennis court and he walked at the same speed while going to the tennis court and
while returning, how much time did he spent at the tennis court?
A watch which gains 10 seconds in 5 minutes was set correct at 9 a.m.
When the watch indicated 20 minutes past 7 o’clock the same evening, the true time is:
The watch gains 10 seconds in 300 seconds.
So it gains 1 second in 30 seconds.
Time shown = 10 hours 20 minutes = 620 minutes.
Actual time = 620 − (620 ÷ 30) = 600 minutes = 10 hours.
So true time = 7 p.m.