look at the 2nd dark green shape which is made of 5 boxes compared to the upper one of 4 boxes.

this is a trick. Take out all the grid lines. Measure the areas of  red and dark green colors using a scale. Compare it to the 2nd picture you will get the answer.

ok guys,
let me try to explain this in geometric language.
the slope of the red triangle=p/b= 3/8= 0.375 and
the slope of the green triangle=p/b= 2/5= 0.4
which shows that the hypotenuse of the whole triangle is not a straight line 
(the slopes of individual hypotenuses being not equal)
now, if you place the triangle with greater slope in the bottom and the one with 
smaller slope on the top, it happens to occupy more space beacause of its 
convexity.....notice the small squares in the corner are shaded more in the second 
triangle.
the difference happens to be equal to 1 square unit.

thanks Tregor, it does make sense now

at first glance, i didnt think it was this complicated ...my first guess was it was just a fool play

hey you saved my trip to karachi !

Tregor's logic is pretty much convincing.

However, where did he get the numbers from? He measured?

no copicat,

i did not measure its just the number of small squares in the base and the height of the 

triangles.

nepalibhai,

CD is not a straight line either..please look at my previous post...

I just kept on staring at the triangles to figure out if one was larger than the other. Then scaled the monitor to find the measurement of each sides: it seemed equal.

But when I created the triangles in computer using 12"x12" boxes as grids, and overlapping first triagle boundary to the second one, the difference seemed apparent. See the picture; the dotted line on second triangle is the boundary of the first triangle. The second triangle is bigger in space than the first triangle.

It's a good one. Its a visual trick.

Kaam garda gardai kaam kai software ma halera solution nikaleko ho.. Phursad ko kurai bhayena ni !