Question

how much pure alcohol must be added to 1200 ml of a 20% solution to make its strength 36% ?


the answer of this ques is 380ml
but i don't know how so plz answer the question clearly in detail

Answer 1

alcohol=20% of 1200=240
36% of (1200+x)=240+x
36(1200+x)=24000+100x
43200-24000=100x-36x
19200=64x
x=19200÷64
=300

Answer 2

20% of 1200=20/100×1200=240 ml
let x ml pure alcohol should be added to 240 ml to make it 36% of (1200+x)
240+x=36/100×(1200+x)
240+x=432+9x/25
x-9x/25=432-240=192
16x/25=192
x=192×25/16=25×12=300ml