Question

5kg of an alloy of lead and tin contains 60% lead how much lead must be added to it to make it 75% lead

Answer 1

60% of 5000g (5kg)

60 * 5000 = 300000

300000/100 = 3000g (3kg) of lead.

if 3000g is 60% how much will 75% be ?

3000g : 60%

  ?       :  75%

We cross multiply.

75 multiplied into 3000 divided by 60 gives you 3,750g (3.75kg)

OR

3000g : 60%

   ?       : 1%

3000/60 = 50

we found that 1% is 50g

so 75% will be -

50*75 = 3750g (3.75KG)

So the answer will be:

3750-3000 = 750g

Therefore 750g (0.75kg) of lead must be added to make its percentage change from 60% to 75%