Posted by Anonymous on .
A man buys 2pens and 4 pencils and gives a hundred rupees note to shop keeper . Shopkeeper ask him to pay Rs10 more to take 4pens and 2pencils. If he bought 2pens and 3pencils how much would the man get back from shopkeeper?

math 
Reiny,
cost of a pen  x
cost of a pencil  y
2x + 4y ≤ 100
4x + 2y = (2x+4y) + 10
2x  2y = 10
xy= 5
x = 5+y
then back in 2x+4y<100
or x+2y ≤ 50
5+y + 2y ≤ 50
3y ≤ 45
y ≤ 15
cost of 2 pens and 3 pencils
= 2x + 3y
= 2(5+y) + 3y
= 10 + 5y
there are multiple answers
Make a chart showing
x .. y (2x+4y) (4x+2y) (2x+3y)
20 15  100  110  85 , so change is 15
19 18  94  104  80 , so change is 20
etc.
(If we assume that Rs 100 was the exact amount for 2pens and 4 pencils, then
20, 15 is the correct answer.)
e.g.
If he bought 2 pens at 20 and 4 pencils at 15
cost would be 100
Had he bought 4 pens and 2 pencils, cost would be 110 which is 10 more as stated,
so cost of 2 pens and 3 pencils is 85, resulting in change of 15
the same can be done for each of the entries in the chart.