A Strange Clock

Algebra Level 3

Jack has a clock that gains 10 minutes per hour. At midday Jack sets the clock at the right time. He leaves the house and gets home in the evening, when the clock marks "7"; Jack thinks "Actually, it's six o'clock".

What time is when, that night, the clock marks 10:23?

REMEMBER: The clock is analogical

8:54 8:23 9:01 10:44

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11 solutions

Express everything in minutes starting in 0 at midday. Since every 60 minutes are displayed as 70, and 10:23 is 623 minutes after midday, we get 60 70 = x 623 , \frac{60}{70}=\frac{x}{623}, where x x is the actual time. This gives x = 534 x=534 minutes after midday, that is, 8 hours and 54 minutes.

Clock adds 10 mins /hour, which means it adds 1min/6mins.

suppose, the actual time is 9 pm, then the clock must be showing (9 * 10 = 90 mins) more. it should shoe the time 10.30pm. but it shows 10.23pm. it means the actual time is near to 9pm but not accurate 9pm.

that's how i got my answer... 8:54

Adrian Hansen - 7 years, 3 months ago
Laxman Selvam
Mar 1, 2014

At 6 the clock shows 7. Hence at 8 the clock shows 9:20 and at 9 it shows 10:30. hence the answer has to be either 8:54 or 8:23. As the clock gains 10 mins per 60 mins it actually shows (7/6)mins for 1 min. So for 54 mins, it will show 54*(7/6)=63 mins. This 63 mins added to 9:20 gives 10:23 hence the time is 8:54!

Arafa Kamel
Mar 2, 2014

clock gains 10 mins every hours which means 10 mins every 60 mins which means 1/6 min for every minute let time passed from midday is 10:23 which means 623 minutes from midday let time on clock is Y and the actual time is X Y=X+X 1/6 623=X 7/6 so X=623*6/7=534 which is 534/60=8.9 which is 8:54

Shabarish Ch
Mar 2, 2014

First of all, let us express everything in minutes. The clock gains 10 mins every hour, so it gains 10 mins every 60 minutes or 1 minute every 6 minutes.

To express it algebraically, let's say x x minutes have passed after the clock was set correctly. During this time, the clock gains x 6 \frac{x}{6} minutes. So even though only x x minutes have passed, the clock shows x + x 6 x + \frac{x}{6} minutes have passed.

In this case, the clock shows 10:23, which means 623 minutes have passed after the clock was set correctly. We suppose that x x minutes have passed in reality. So,

x + x 6 = 623 x + \frac{x}{6} = 623

7 x 6 = 623 \frac{7x}{6} = 623

x = 534 x = 534

Converting this back into hours, we get 8 hours and 54 minutes. So, 8:54 is the correct time.

Taisir Mahmud
Apr 5, 2014

The clock shows 60 min more after 7 hours. So using unitary method, in (7 * 60) min it shows 60 min more So, in (3 * 60+23=203) min its shows (60 * 203)/(7 * 60)= 29 min more.

But at 6 the clock was showing 7, so clock was one hour fast beforehand. So in total, at 10:23 the clock is showing 1hr and 29 min more than it actually is. So, at 10:23 actual time is 8:54

Azmain Yousuf
Mar 21, 2014

At 6 it shows 7.So, at 8 it shows 9:20.At 9 it shows 10:30. Actually 7/6 mins for 1 min.For 54 mins it shows 54*(6/7) min=63 mins.Now,if 63 mins is added to 9:20 its 10:23.thus the time is 8:54.

                                         [SOLVED]

Cool Idea

Azmain Yousuf - 7 years, 2 months ago
Mahendar Singh
Mar 20, 2014

6 --> 7; 7 --> 8:10; 8 --> 9:20; 9 --> 10:30;

actual clock display = 10:23, hence time should be just little less than 9:00.

Brute Force applied. SORRY ALGEBRA

Harshal Khachane
Mar 8, 2014

for every 60 min. clock shows 70 min.

ratio=6:7

now clock is 10.23==10x60+23=623 min.

6:7=x:623

x=534min

534 min=8hr+54min.

Krishna Garg
Mar 4, 2014

Since clock goes 10 mts slow each hr,From &.07 PM to to 10.23 PM in the clock it is 3 hrs and 23 mts later. but at 7 Pm it was actually 06:00 PM, therefore calculating 10 mts slow/hr ,it will be 08.54 Ans

K.K.GARG,INDIA

Tanveer Hussain
Mar 4, 2014

x/623=6/7 x=534 8:54

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