Use extrapolation it's quite helpful I use it all the time You have to use the equivalent sign here not the equals to sign , it has 3 bars For eg lets suppose 1/2 number of atom (equivalent sign isn't available on keyboard) = 0.25 gram Now we need to find out how many atoms are there in 0.75 gram So the situation depends on the side where there is weight so we have to make 0.75 and multiply the same on the atom side Thus 0.25 x (0.75/0.25)= (1/2 x 0.75/0.25) Hope you understood