Chitra657 wrote:
Bunuel wrote:
The figure above shows the circular cross section of a concrete water pipe. If the inside radius of the pipe is r feet and the outside radius of the pipe is t feet, what is the value of r ?
(1) The ratio of t - r to r is 0.15 and t - r is equal to 0.3 foot.
(2) The area of the concrete in the cross section is 1.29π square feet.
Attachment:
2014-12-23_1815.png
VeritasKarishma Bunuel ScottTargetTestPrepIn sums like these, especially stat 2, we get (t+r)(t-r)= 1.29
Now I assumed that various numbers can fulfill the condition, so insuff.
But, on some DS problems, it turns out that statements like these sometimes have only one set of correct value.
So under time pressure, how to decide whether to mark insuff and move on or try plugging a few different values and check?
Chitra657When you have no constraints on the values the variables can take, an equation with two or more variables will give you multiple solutions.
Say a + b = 10
a can be 9.1 so b will be 0.9
a can be 11 so b will be -1
a can be 5 so b will be 5
and so on...
There will be infinite values.
But what if you are given that a and b must be positive integers. Then you have limited solutions: a = 1, b = 9; a = 2, b = 8 ... till a = 9, b = 1.
Now what if you are given further than a < b? Then you have still fewer solutions: a = 1, b = 9; a = 2, b = 8; a = 3, b = 7, a = 4, b = 6
Now what if you are given that a and b both are perfect squares too? Then there is only one solution a = 1, b = 9
Hence, when trying to figure out whether an equation in multiple variables has a unique solution or many solutions, you need to look at the other constraints mentioned.
Check this post:
https://www.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/2011/0 ... -of-thumb/