Prime Time

Before 10, there are $4$ prime numbers $(2,3,5,7)$ , now before 10:00 am, 7:00 am comes, so the time between 7:00 and 8:00 is our required time since the hour part should be $7$ . Now, for the minute part, it cannot be greater than $59$ . So, we can rule out $72,73,75,77$ for the minute part of the time. The minute part should start with $5$ then as it is the prime number lower than 7 and is valid. So, we come down to 4 choices --- 7:52 , 7:53 , 7:55 and 7:57 am . We can clearly see that 7:57 am is the last time which fits the criteria of this question. So, $\boxed{7:57 am}$ is our required time.

The last hour it can be is 7 (the last prime number before 10). The last prime digit in the tens place (for minutes) that it can be is 5 (the last prime before 6; there are 60 minutes in an hour.) The last minutes digit it can be is 7 (the last prime before 10). The answer is $\boxed {7:57}$

We can follow a digit based approach. 1. Let the time is X:XX

2. Let's fill the hour which is prime and closely less than 10. Ans is "7".

Ans:7:XX

3. Now its minute's digit turn. digit which is maximum(ie. we need to get close to 10am) and prime possible is "5". because maximum minutes possible is 60.

Ans:7:5X

4. Now for the last digit the maximum prime possible is "7".

Ans:7:57

Yeeeeee........... YOU GOT IT........

7- the closest prime no. to 10. 5- the closest prime no. to 6 (as in 60). 7- the closest prime no. to 9 ( as in 59 minutes).

biggest below 59 minutes is 57 and the biggest below 10 is 7 so it becomes 7:57

before 10 am , the largest prime number is 7 , so combinations are 7:53 , 7:55 , 7:57. we see the last one is 7:57.

before 10...(2,3,5,7) are the prime nos.. so nearest to 10 is 7,sogo from 7:59 in reverse..u will hit on 7:57..wich has all prime nos.

2,3,5,7 are prime numbers before 10 .So, we need to arrange a number(time) with 2,3,5,7 so that only 1 & itself can divide it.The number is 757 or 7:57 which is a prime time.[As it is closest to 10:00]

                                          (SOLVED)

there 4 prime no. 2,4,5,7. So now combine them. And is 7:57 am

0757

within 10 the prime numbers are 2,3,5,7 After 2.22 , the last possible before 10 am is 7.57

The prime numbers before 10 are 2,3,5 and 7. Since 7 is the greatest among these, the time will belong to the 7th hour. Since there are only 60 mins. in an hour, thus time will be 57 minutes, which is the largest number less than 60 and is formed of two prime numbers. Thus, the time will be 7:57 am

the answer is 7:57

which having all digits as prime number before 10am

Before 10, 9 is not prime, nor 8.

Hence 7.

Start from 7:60 (i.e. 8)

7:59.........discarded because of 9

7:58.........discarded because of 8

7:57......... Ha, Gotcha.

7:57 is the only time before 10:00 where all 3 digits are prime numbers.

go through all prime numbers ....... i.e 2,3,5,7,11 and so on... but before 10:00 am ...... so less than 10 .... that is reverse order from 10 which gives you 7. Than in digital clock or any clock minutes are never 70+ .... so less than 7 is 5... so 7:57 am is the correct answer . :D

You just have to go back from the digit 10 and 7 comes first..(7:??) then we have to decide with the minutes deciding back from 6 which is 5 (7:5?) and the last place from digit 9 i.e, 7 of course so the answer is (7:57)

7 is the highest prime before 10, 5 is the highest number before 6 and 7 is the highest prime number before 9 so it’s 7:57

Prime numbers smaller than 10 are $2,3,5,7$ so it gives us $7:77$

But the minute number is smaller than 60.

So the answer is $\boxed{\large{7:57~\text{am}}}$

Before 10am, it is 9:59, yet 9 isn't prime. Do it cannot be 9:something. This holds true for 8, and the next option is 7:something. 7 is prime, so this works. The last ten minutes if 7:something are 7:5x and 5 is a prime, so this is our solution. The highest prime under 10 us 7, so x is 7.

Is the the last number before 10 is 7 and then you have a to think of there is 60 minutes in an hour. So that would have to be before the 6 which the only prime number is 5 then you need see which prime number are before 9 which is 7 again

We have four prime numbers between 1 and 10(2,3,5 and 7) .By this we statement we come to know that the time is between 7 and 8.It is now easier because by this statement we know that the time is between 7.50 and 8.00.the highest prime number in between is 57 .There fore the time is 7.57 a.m

The answer is 7.57am. 9 and 8 are not prime numbers but 7 is.

common sense

From 10, think of a lower prime number for each digit.

Its 7:57.. Simple

7:57 AM

The only prime numbers available before 10 is 2,3,5,7. Out of this 7 is the biggest and 7am is the last prime number before 10. So the answer lies some where in 7am. In an hour there is only 60 minutes so, the largest prime number before 60 is 57. Thus the obvious answer is 7:57am.

Hope you understood.

the prime numbers before 10 are: 2, 3, 5 & 7, so the nearest hour before 10 is 7am, and the last minute is 57min, not 58 or 59 since 8 & 9 are composite numbers

We know that there largest prime below $10$ is $7$ . We want the time which has the most primes. So, we start at the top and work our way to the bottom. Therefore, we start in the $7:5x$ . The largest prime, once again, in the tens is $7$ . So the answer has to be $7:57$ or in other words, $\boxed{757}$ .

(prime no is=1,2,3,5,7 ).A.TO.Q. 2:22 is a time in which all no. are prime no.

now, we take the prime no.which is before 10. 7 is the no. we have to taken,the time a.to watch time will be 7:11,7:13,7:15 ......... 7:57

I actually got it right on the third try.

First answer: 777 That's dumb isn't it ? :D the clock never strikes 7:77 AM !

second answer: 555 After the first embarassment I tried a face saver.. and splat! egg on my face again..

the answer of course was 7:57 AM The highest single digit prime number is 7. That figures on the clock too.. so there is your first digit. the minutes range from 0 to 59. so the highest single digit prime that can fit in to the first minutes spot is 5. The second digit for the minutes has to be <=9. 9 & 8 can be ruled out and that leaves us with 7.

so there you are: 7:57 AM

for given problem solution must contain three prime numbers which should not exceed 60 in seconds place and also should not exceed 10 in hours place. so in hours place 7 is highest prime before 10, 57 is highest prime before 60. finally 7:57 is answer.

Lets take 10:00 am as the no.10. The last prime no. before 10 would be 7. The largest combination in terms of 3 digits would be 7:77, but as 70 mins in a hr is not possible, we choose a prime number which immediately precedes 7, which is 5. so the last time before 10:00 am where all digits are prime, would be 7:57.

it seem answer should be 7:77 but there is no time like 7:77 its the 7:57 which is close to 10.00am

since what was asked was what is the last time before 10:00 am when the three digits on the clock are all prime numbers. and so prime numbers are numbers that only 1 and itself are the factors, so to determine, start counting backwards, 9?? no! because 9 is not prime, 8?? still no, not a prime! 7? yes! thats 7 am, we only need to determine the prime minutes to complete the answer..and the two digits should also be prime and below 60... thats why its 57... the answer is 7:57, expressed as 757

It is so simple! First choose the largest prime before 10...which is 7! And the second largest is 5! We cannot use 777, 775(since there is no time with this) The only possible answer 757(07:57)

The last prime number which is smaller than 10 is 7, and because it can't be 7:77 am, (the second number must be smaller than 6) we'll use the next prime number smaller than 6. It is 5. So the answer is 7:57 am.

the last time the digital clock shows all the three prime number digits before 10:00 am is at 7:57 am....hence the answer 757

Before 10:00 all time nos. have three digits, so we need to check the first digit...all the time stamps in the 9th hour do not fit as nine isn't a prime no. Neither is 8. But 7 is. So we start from back, 7:59, no ; 7:58, no ; 7:57, yes.