Official Quant thread for CAT 2013

scarecrow28 · February 13, 2013, 2:52pm

@prateek987 said:
@ScareCrow28 Sir..I want to know some thing...I have a book called m tyra quicker mathematics ...its this book gud...? it has a lot of shortcuts....From which do you practice ...?

Bhai mere I'm no sir..please 😃 Yar maine first time suna hai is book k bare me. And I never practice from any book. For CAT I never took a book and started solving questions. I practice from forums or test papers or PG or puzzles and riddles but never from any particular quant book. Sorry can't help you on this matter :(

exodia · February 13, 2013, 3:10pm

Find all numbers of the form of 56x3y that are divisible by 36.

meenu05 · February 13, 2013, 3:18pm

find the ratio of the 17th terms of the a.p if the ratio of the sum upto 'n' terms of the progressions is ( 3n+2) : ( 4n-13) ?

akashgupta1987 · February 13, 2013, 3:19pm

@ScareCrow28 pranaam _/\_ abse hum bhi yahi milenge. 2013-2014 apna hoga

P.S. Sorry for the spam :)

scarecrow28 · February 13, 2013, 3:21pm

@Exodia said:
Find all numbers of the form of 56x3y that are divisible by 36.

56x3y should be divisible by 36 = 4*9

For it being divisible by 4, y should either be 2 or 6

For, y=2 only x=2 is possible

For y=6 only x=7 is possible

Hence only 2 values possible!

@akashgupta1987 said:
@ScareCrow28 pranaam _/\_ abse hum bhi yahi milenge. 2013-2014 apna hoga P.S. Sorry for the spam

Pranaam bhai _/\_ :)

scarecrow28 · February 13, 2013, 3:26pm

@meenu05 said:
find the ratio of the 17th terms of the a.p if the ratio of the sum upto 'n' terms of the progressions is ( 3n+2) : ( 4n-13) ?

(3n+2)/(4n-13) = [2a1+(n-1)d1]/[2a2+(n-1)d2]

Put, n=33...Ans should be = 101/119? ...

meenu05 · February 13, 2013, 3:34pm

@ScareCrow28 the answer is 101: 119

scarecrow28 · February 13, 2013, 3:37pm

@meenu05 said:
@ScareCrow28 the answer is 101: 119

Edited..We have to put n=33

sbharadwaj · February 13, 2013, 3:44pm

@jashholmes said:
In a city 60 % of the population owns a car, 75 % owns a rickshaw, 80 % owns a scooter, and 95% owns a bicycle, what person at least owns all four of them???

40%..?

jashholmes · February 13, 2013, 3:45pm

@sbharadwaj no!!!

akashgupta1987 · February 13, 2013, 3:46pm

@saurav205 said:
24..???

@ScareCrow28 yar change in avg se nikalna hai na? zara approach batao...is it 6/n=1/4??

sbharadwaj · February 13, 2013, 3:46pm

@sonamaries7 said:
The sum of the cubes of any 3 consecutive nos is always divisible by:18279none

9..! Take 1,2,3 n 2,3,4..

scarecrow28 · February 13, 2013, 3:48pm

@akashgupta1987 said:
@ScareCrow28 yar change in avg se nikalna hai na? zara approach batao...is it 6/n=1/4??

Diff in total = +6

Diff in Avg = +1/4 = +6/24

Hence there are 24 people..

nole · February 13, 2013, 3:51pm

If A= 10 ! + 12! + 14!........ 100! . Then find the highest power of 2 in A. How to solve this ?

chirpibird · February 13, 2013, 3:54pm

@meenu05 said:
find the ratio of the 17th terms of the a.p if the ratio of the sum upto 'n' terms of the progressions is ( 3n+2) : ( 4n-13) ?

(3n+2)/(4n-13) = [2a1+(n-1)d1]/[2a2+(n-1)d2]
put n=33

this i did because.. 17th term will be a1+16d1 .... to get 2 common out of the brackets,33 would work.
ans: 101:119

estallar12 · February 13, 2013, 3:56pm

@nole said:
If A= 10 ! + 12! + 14!........ 100! . Then find the highest power of 2 in A. How to solve this ?

A mod 2^9 = 256.

A mod 2^8 = 0.

So, Highest Power = 8.

A = 10! ( 1 + 11 + 11*12 + ... ).

So, we need to find powers of 2 in 10! which is 8.

chirpibird · February 13, 2013, 3:58pm

@jashholmes In a city 60 % of the population owns a car, 75 % owns a rickshaw, 80 % owns a scooter, and 95% owns a bicycle, what person at least owns all four of them???

and 20%???

... sry .. it's 10%

nole · February 13, 2013, 3:59pm

@Estallar12 I didn't get your explanation.can you please explain again. I tried it solving by finding the total sum and then trying to divide by 2 ( i couldn't do that coz finding total sum was difficult) . A must be a big number,how can 2^8 be the highest power. ? I mean that means 256(2^8) * k = A where K is not divisible by 2. isn't it ?

chirpibird · February 13, 2013, 4:03pm

@jashholmes In a class, two students weighing 54 and 62 kgs are replaced by two new students weighing 58 and 64 kgs. As a result the average weight of the class increases by one fourth of kg. How many students are there in the class???

24

t=total, A avg, N=number of students
t/n=A
(t+6)/n=A + 1/4
or 6/n=1/4
n=24

sbharadwaj · February 13, 2013, 4:05pm

@Estallar12 said:
A mod 2^9 = 256.A mod 2^8 = 0.So, Highest Power = 8.A = 10! ( 1 + 11 + 11*12 + ... ).So, we need to find powers of 2 in 10! which is 8.

Nice soln..

Bhai I have a doubt..

We got A = 10!( Sum of something say X).. Now there's a possibility that X may add up to a 2's multiple..in which case, answer may differ..!

Plz correct me if I'm wrong..