Posted by **Anonymous** on Saturday, May 21, 2011 at 8:32am.

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**, Saturday, May 21, 2011 at 9:28am
cost of a pen --- x

cost of a pencil -- y

2x + 4y ≤ 100

4x + 2y = (2x+4y) + 10

2x - 2y = 10

x-y= 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.

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