ms1 = 150g, c1% = 20%
ms2 = 600g, c2% = 40%
din c% = mdx100/ms
=> md1 = ms1xc1/100 = 150x20/100 = 30g
=> md2 = ms2xc2/100 = 600x40/100 = 240g
=> md.final = md1+md2 = 30+240 = 270g
ms.final = ms1+ms2 = 150+600 = 750g
=> c%.final = md.finalx100/ms.final
= 270x100/750 = 36%