In a purse there are 30 coins, twenty one-rupee and remaining 50-paise coins. eleven coins are picked simultaneously at random and are placed in a box. if a coin is now picked from the box, find the probability of it being a rupee coin?
option 1 : 4/7 option 2 : 1/2 option 3 : 2/3 option 4 : 5/6

what is the original number? you forgot to add it.

geometry: triangles

solvers

lessons

answers archive

call the larger triangle abc

then the smaller triangle cde is similar to abc (all angles are equal, aaa).  

ab is the side that is 36, and we wish to find de, the side corresponding to ab

area_cde = area_abc - area_cde --> area_abc / area_cde = 2

let x=length of de

ratio of areas = (ratio of sides)^2

+2+=+%2836%2fx%29%5e2+

+2+=+1296%2fx%5e2+

++x%5e2+=+1296%2f2+=+648+

25.45584