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TSD Doubt
by RUPALI GOYAL - Monday, 22 September 2014, 11:27 AM
  A group of 10 men can do a job in 15 days. The group starts working and after every three days they are joined by two more men. On which day does the job get completed?

a) 10th
b) 11th
c) 12th
d) 13th
Re: TSD Doubt
by RUPALI GOYAL - Monday, 22 September 2014, 02:20 PM

could you please help in following problem also:

Two motorists Anil and Sunil are practicing with two different sports car on a circular tract. Both start from the same point on the circular track. Anil completes 1 round in 1 min and Sunil takes 2 min to complete a round. While Anil maintains the same speed for all rounds, Sunil halves his speed after the completion of each round. How many times Anil and Sunil will meet between the 6th and 9th round of Sunil (6th and 9th excluded)? Assume the speed of Sunil remains constant throughout each round and changes after completion of that round.

a) 260
b) 347
c) 382
d) None of these

Solution: Sir, I calculated as follows and got 382 as answer. However, the ans is d. Please tell me what did I do wrong.

Let Anil speed = a
Then Sunil speed will be a/2

In 7th round Sunil speed will be a/27 and in 8th round the speed will be a/28
. So, the no. of times Sunil meets Anil in 7th round is 127 and in 8th round, it is 255.

Total no. of times = 127+255=382.

Re: TSD Doubt
by R. kumar - Thursday, 16 October 2014, 09:54 PM

Try if this works for you.

going by your assumption :

Let Anil speed = 2a
Then Sunil speed will be a  (whole nos are easier to deal with)

and the respective times to complete one round be t1= 1 & t2= 2 mins.

So the time taken By Sunil to complete the 6th & 7th rounds are :

t1 * 2^6 =64  +  t2 *2^7=128 which is 192 mins.

Since Anil covers 1 round in 1 min ,he will meet Sunil  1*192 times.

Re: TSD Doubt
by tgdel1208 tg - Monday, 20 October 2014, 07:04 PM
  total man days required to do the job =150,1 man can do 1/150th work in a day,now apply this for first 3 days,then next 3 days and so on or else use lcm method