Official Quant thread for CAT 2013

@ishu1991 said:
yes u ar ryt plss explain
gimme some time.. will upload a diagrm.. it'll be easier to look and understand
@joyjitpal said:
find the sum of the following seriesS = 7/6 + 13/12 +21/20 +31/30 +.........+ 9901/9900
S=1+1/6 +1+1/12 + 1+1/20 +..... + 1+1/9900
S=1+1/2.3 +1 +1/3.4+....+1+1/99.100
S=98*1 + 1/2 -1/3 +1/3-1/4 + .....+1/99 -1/100
S=98+1/2-1/100
S=98+49/100
S=98.49
@joyjitpal said:
find the sum of the following seriesS = 7/6 + 13/12 +21/20 +31/30 +.........+ 9901/9900
9849/100
@joyjitpal said:
240
approach please...?
@joyjitpal said:
find the sum of the following seriesS = 7/6 + 13/12 +21/20 +31/30 +.........+ 9901/9900
98.49
Nth term=n2+3n+3/ n2+3+2
=1+1/n2+3n+2
=1+1/(n+1) -1/(n+2)
Sum of series till 98th term=98+1/2-1/100=98.49

@joyjitpal said:
find the sum of the following seriesS = 7/6 + 13/12 +21/20 +31/30 +.........+ 9901/9900
s = 7/6 + 13/12 + 21/20 + ..........9901/9900
= 1 + 1/6 + 1 + 1/12 + ............1 + 1/9900
= 98 + 1/2 - 1/3 + .........1/99 - 1/100
= 98 + 1/2 - 1/100
= 98 + 49/100
= 98.49 ?
@saurabhlumarrai said:
in an attempt to find the prime number between(and including) 101 and 1000,all the numbers from 101 to 1000 are written on a sheet of paper.the first three steps of the process involve crossing out all multiplesof 2,3 and 5.After these three steps,how many numbers are left uncrosed?a)230b)235c)240d)245
2k form -> 102,104,...,1000 = 450 numbers
3k form -> 102, 105,...,999 = 300 numbers
5k form -> 105,110,...,1000 = 180 numbers
(2*3)k form -> 102,108,...,996 = 150 numbers
(2*5)k form -> 110,120,...,1000 = 90 numbers
(3*5)k form ->105,120,...,990 = 60 numbers
(2*3*5)k form -> 120,150,...,990 = 30 numbers
hence, total multiples of 2,3 and 5 = 450+300+180-(150+90+60)+30 = 660...
numbers that are left -> 900-660 = 240....
@DeAdLy -post the solution plz.....m not able to solve it..
@ishu1991
here.. if u dont get it, PM me. :)

110) What is the sum of all positive rationals p/30 (in lowest terms) which are less than 10?(a) 360 (b) 400 (c) 450 (d) none of the foregoing
@saurabhlumarrai said:
approach please...?
(990*1/2*2/3*4/5 +2 ) - (90*1/2*2/3*4/5 +2) gives 240

colonel major and general started a work for rs 816. colonel and major did 8/17 of the total work , while major and general did 12/17 of work. what is the amount of the least efficient person?

@saurabhlumarrai said:
in an attempt to find the prime number between(and including) 101 and 1000,all the numbers from 101 to 1000 are written on a sheet of paper.the first three steps of the process involve crossing out all multiplesof 2,3 and 5.After these three steps,how many numbers are left uncrosed?a)230b)235c)240d)245
multiples of 2 = 450
multiples of 3 = 300
multiples of 5 = 180
multiples of both 2 and 5 = 90
multiples of 3 and 5 = 60
multiples of 2 and 3 = 150
multiples of 2 , 3 and 5 = 30

no.s left uncrossed = 900 - 450 - 300 - 180 + 150 + 90 + 60 - 30 = 240 ?
@ChirpiBird said:
@ishu1991here.. if u dont get it, PM me.
awusum dude hats off to u
@vbhvgupta said:
colonel major and general started a work for rs 816. colonel and major did 8/17 of the total work , while major and general did 12/17 of work. what is the amount of the least efficient person?
1/C+1/M+1/G = 1
1/c+1/M = 8/17
1/m+1/g = 12/17
adding above 2 and sub in the first
1/m = 20/17-1 = 3/17
and he is the least efficient
bhak sala
@vbhvgupta said:
colonel major and general started a work for rs 816. colonel and major did 8/17 of the total work , while major and general did 12/17 of work. what is the amount of the least efficient person?
3/17?
Q.
There are two containers each having balls of two colours, green and red. The ratio of the green balls to the red balls in the first container is 2 : 3 and in the second container it is 2 : 1. N balls are randomly picked from the first container and transferred to the second container. The ratio of green balls to the red balls in the second container now becomes 1 : 1. However, the ratio of balls in the first container remains 2 : 3. If the number of balls in the first container is 25, then the value of N for which the final number of balls in the second container becomes 24 is


a)5

b)10


c)15


d)20
@ishu1991 said:
110) What is the sum of all positive rationals p/30 (in lowest terms) which are less than 10?(a) 360 (b) 400 (c) 450 (d) none of the foregoing
none of these?
1/30 + 2/30+ 3/30 + ... 299/30
1/30 (1+2+3+... 299)
1/30*((299* 300)/2)
= 299*5= 1495??

@joyjitpal said:
(990*1/2*2/3*4/5 +2 ) - (90*1/2*2/3*4/5 +2) gives 240
can u please elaborate this relationship-990*1/2*2/3*4/5...i mean to say why multiplied only with 1/2*2/3*4/5.can it be something else for different digit, like the same question changes to 2000 then what will be the multiplicative factor...??
@joyjitpal said:
Q. There are two containers each having balls of two colours, green and red. The ratio of the green balls to the red balls in the first container is 2 : 3 and in the second container it is 2 : 1. N balls are randomly picked from the first container and transferred to the second container. The ratio of green balls to the red balls in the second container now becomes 1 : 1. However, the ratio of balls in the first container remains 2 : 3. If the number of balls in the first container is 25, then the value of N for which the final number of balls in the second container becomes 24 isa)5b)10c)15d)20
15??
options se karlo bhai ye wala toh...

btw joyjit bhai...V ke fan ho aap 😁