# Aptitude - Clock - Discussion

Discussion Forum : Clock - General Questions (Q.No. 7)
7.
At what time between 5.30 and 6 will the hands of a clock be at right angles?
 43 5 min. past 5 11
 43 7 min. past 5 11
40 min. past 5
45 min. past 5
Explanation:

At 5 o'clock, the hands are 25 min. spaces apart.

To be at right angles and that too between 5.30 and 6, the minute hand has to gain (25 + 15) = 40 min. spaces.

55 min. spaces are gained in 60 min.

 40 min. spaces are gained in 60 x 40 min = 43 7 min. 55 11

 Required time = 43 7 min. past 5. 11

Discussion:
74 comments Page 1 of 8.

Manish Badgal said:   12 months ago
Hour hand moves = 0.5 degrees/min.
Minute hand moves = 6 degrees/min.
The angle between the hour hand and the minute hand should be = 90 degrees.
Let the minutes at which hour and minute hand makes 90 degrees = x.

Therefore,
Minute hand angle - hour hand angle = 90 degrees.
6 degree/min * x - (5*60 mins + x) * 0.5 degree/min = 90 degrees.
6 degree/min * x - 150 degrees - x * 0.5 degree/min = 90 degrees.
(6 degree/min * x - x * 0.5 degree/min) = 90 degrees + 150 degrees.
(6 degree/min * x - x * 0.5 degree/min) = 90 degrees + 150 degrees.
5.5 degree/min * x = 240 degrees.
x = 240 mins / 5.5
x = 43.6363 mins.

Hence, at time 5 hour and 43.6363 mins hour hand and minute hand makes 90 degrees angle.
(2)

Ash said:   2 years ago
@All.

My doubt is here the question is between 5:30 & 6.

So, for 90degress it's should be 5:45 right? Why did they assume from 5'o clock?
(14)

Renuga said:   2 years ago
At what time between 5 and 60' clock the hands of a clock will make an angle of 40%?

Ankita said:   4 years ago
@Abi and @ Babu.

When two hands coincide after exactly one hour, minutes hand travels one full circle that is 60 spaces but hours hand moves 5 space forward. So after exactly one hour later, they gain 55 spaces are their relative gain.
(2)

Diksha Mishra said:   4 years ago
Please, someone, share the solution of how come40*60Ã·55 = 7Ã·11 came ? Pls someone explain it..

Babu said:   4 years ago
55min spaces are gained in 60min. What it is, Can someone explain to me?

ABI said:   4 years ago
55min spaces are gained in 60min. What it is, Can someone explain to me this?

Ajay said:   4 years ago
Thank @Ajay.

Swathi sayyapureddy said:   5 years ago
@Shree.

When hour hand is preceding minute hand then theta=30H~11M/2 will be used otherwise, means when min hand is preceding hour hand then theta=11M/2~30H can be used.

Dipankar Mondal said:   5 years ago
40 * 12/11 = 43 7/11.
(2)