Mobile phones

[treker]

2003 2004
Model A 190 175
Model B 200 205
Model C 210 220

The table above shows quantities for various models of mobile phones sold by a retailer. Assuming prices did not change between 2003 and 2004, was the total revenue from sales in 2004 greater than the total revenue in 2003?
(1) Model A is the most expensive phone.
(2) Model C is the least expensive phone.

How do we solve such questions under 2 minutes?

-treker

[phanideepak]

so rephrasing the question (175x + 205y + 220z) - (190x + 200y +210z) > 0

i.e -15x + 5y + 10z > 0

-3x + y + 2z > 0

case 1 : x > y,z consider x = 101 z = 100 y = 99 so -303 + 200 + 99 < 0

Consider x = 101 z = 100 y = 100 so -303 + 200 + 100 < 0

Sufficient

case 2 : z < x,y consider x=101 y= 106 z = 100 so -303 + 106 + 198 > 0

Consider x = 101 y = 100 z = 99 so -303 + 100 + 198 < 0

Insuff

So IMO answer is
A

[amit2k9]

good approach using algebra.