board counting from top and bottom

enriqueta26 wrote:Could somebody help me with this one?

2oth board counting from the top is immediately below the 16 th board counting from the bottom. How many board members are there?

answer: 34

Thank you so much!!

now
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20 15 so this 2 are overlappin so we will have 20+16-2 =34
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Hi enriqueta,

Building the model as amising did is one way to do this question. On the test you don't actually have to draw all the boards of course. Solving requires little more than careful step by step.

An alternative is to think through it logically.
20th from top is below the 16th from bottom means that the 16th from the bottom is actually the 19th from top

The 18th from top must be the 17th from bottom
The 17th from top must be the 18th from bottom
. . .
. . .
. . .
1st from top must be the 34th from bottom.

There are 34 boards.

An illustrated solution as well as a step by step video solution is available at GMATPrep Question 1413

Good luck,
-Patrick

thank you so much!!!!

You're so welcome!

Shortest soln. could be this..U have to just visualize in mind...

20th board from top is immediately below 16th board from bottom
i.e. 20th board from top is 15th board from bottom.
so there are 14 board below 20th from top.. Total = 20 +14 = 34.