math
posted by Ajay .
In a school 1/5 th of the girls and 1/8 th of boys took part in a school camp. Find friction of the total strength of took part in the camp

We would have to know how many boys and girls there were.

Well if 1/5th of the girls and 1/8th of the boys when we put this as a whole fraction, we get 13/40th of the grade went to the camp. We do this by making both fractions have a common demoninator (bottom) then simply adding them to find fraction of boys and girls(all of the grade)

That won"t work. Just test it with 2 very different amounts.
Let's assume there are 1000000 boys and 5 girls. 1/8 of 1000000 is 125,000. 1/5 of 5 is 1. So 125,001 out of 1,000,005 people went. That is (a little more than) 12.5%. Your fraction of 13/40 is 32.5% and I am not quite sure of the reasons why you picked that method.
Using different numbers, assume there are 8 boys and 5 girls. That's 2 people out of 13. That's 15.38%. That's quite different from our other number.
The ONLY way to do this is to assume (quite poorly) that the number of boys and girls are even. OR to find out how many of each there are. At least that's all I can think of unless I am having a stupid moment, which I am known for. :)