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Question

Rahman bought 30 stamps consisting of 20 paise and 30 paise stamps. Given that the stamps cost Rs.7.80 altogether, how many 20 paise stamps did he buy?

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Solution

The correct option is **A** 12

Rahman bought 30 stamps consisting of 20 paise and 30 paise stamps and total stamps cost Rs 7.80.

Rahman bought 30 stamps consisting of 20 paise and 30 paise stamps and total stamps cost Rs 7.80.

Let 20 paise stamps are x and 30 paise stamps are y

Then x+y=30 ............. (i)

Cost of 20 paise stamps =0.20x

Cost of 30 paise stamps =0.30x

But total cost of stamps is Rs 7.80

Then, 0.20x+0.30y=7.80 ............. (ii)

Multiply (ii) by 10, we get

0.20x×10+0.30y×10=7.80×10

2x+3y=78 ............... (iii)

Also, from (i)

3×x+3×y=3×30

⇒3x+3y=90.............. (iv)

Subtract (iv) with (iii), we get

(3x+3y)−(2x+3y)=90−78

⇒3x+3y−2x−3y=12

⇒x=12

Then 20 paise stamps are 12.

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