3 parts are grey and 1 part is black. This means there are 4 parts in total. Therefore the black fraction is 1/4. Multiply this by 100 to get the percentage: 100*1/4 = 25%
3 parts are grey and 1 part is black. This means there are 4 parts in total. Therefore the black fraction is 1/4. Multiply this by 100 to get the percentage: 100*1/4 = 25%