yes formatted soul is right for your 2nd questine.

the difference between 18 and 24 is minos 6 haha lol.

24 karat means 99.9 percentage of pure gold (3 nines are fine) he he.
22 karat is 91.66 percent pure gold and balance 8.34 percent will be all other metals like copper(impurities)91.66 is equal to division of 22 by 24( when 99.9 percent is 24 karats.)

now lets come to 18 karats is 75 percent pure gold bal 25 is impurities. 75 is equal to division of 18 by 24

this is true.

i hope your head is rolling take hot tea and read again.

bye.