Virus VS Worm

karthikpandian19 wrote:All 250 files on Sam's hard drive are infected by either a virus or a worm or both. The number of files that are infected only by a worm is 2.5 times the number of files that are infected by both a virus and a worm. If 50% of the files were not infected by a virus, how many of Sam's files were NOT infected by a worm?

50
70
75
100
125

Let No of files affected by both Virus and worm be x
No of files affected by worm only = 2.5 x

If 50% of the files were not infected by a virus

2.5x = 250/2
2.5x = 125
x = 50

how many of Sam's files were NOT infected by a worm?

y + x + 2.5x = 250
y + 50 + 125 = 250
y = 250 - 175 = 75

Option C

I am bit confused on this subject / explanation.

Can you explain please???

rijul007 wrote:

karthikpandian19 wrote:All 250 files on Sam's hard drive are infected by either a virus or a worm or both. The number of files that are infected only by a worm is 2.5 times the number of files that are infected by both a virus and a worm. If 50% of the files were not infected by a virus, how many of Sam's files were NOT infected by a worm?

50
70
75
100
125

Let No of files affected by both Virus and worm be x
No of files affected by worm only = 2.5 x

If 50% of the files were not infected by a virus

2.5x = 250/2
2.5x = 125
x = 50

how many of Sam's files were NOT infected by a worm?

y + x + 2.5x = 250
y + 50 + 125 = 250
y = 250 - 175 = 75

Option C

Heres another explaination

Lets say
number of files affected by Virus only = A
number of files affected by Worms only = B
Affected by both = C

A + B + C = 250

The number of files that are infected only by a worm is 2.5 times the number of files that are infected by both a virus and a worm.

B = 2.5C

If 50% of the files were not infected by a virus,

This means 50% are affected by worms only = B = 250/2 = 125

how many of Sam's files were NOT infected by a worm?

You are asked to find the number of files affected by Virus ONLY = A = 250 - (B+C) = 250 - (125 + 50 ) = 75

Thank you....now got it...

rijul007 wrote:Heres another explaination

Lets say
number of files affected by Virus only = A
number of files affected by Worms only = B
Affected by both = C

A + B + C = 250

The number of files that are infected only by a worm is 2.5 times the number of files that are infected by both a virus and a worm.

B = 2.5C

If 50% of the files were not infected by a virus,

This means 50% are affected by worms only = B = 250/2 = 125

how many of Sam's files were NOT infected by a worm?

You are asked to find the number of files affected by Virus ONLY = A = 250 - (B+C) = 250 - (125 + 50 ) = 75

OA is 75