1. If the price of pen decreases by 20%, then a man can buy 10 more pens for Rs 100. What is the new price (in Rs) of each pen?
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By: anil on 05 May 2019 01.48 am
let initial price = x let he buy y number of pens for 100. $$Rightarrow x imes y= 100$$. If the price of pen decreases by 20%, then a man can buy 10 more pens for Rs 100
$$Rightarrow (frac{100-20}{100} imes x) imes (y+10)= 100$$ $$Rightarrow (0.8 imes x) imes (y+10)= 100$$
$$Rightarrow (0.8x imes y)+(80 imes x)= 100$$
$$Rightarrow (80)+(80 imes x)= 100$$
$$Rightarrow (80 imes x)= 100-80 = 20$$
$$Rightarrow x= frac{20}{8} = 2.5$$/-
new price = $$0.8 imes x = 0.8 imes 2.5 = 2$$/- so the answer is option B.
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$$Rightarrow (frac{100-20}{100} imes x) imes (y+10)= 100$$ $$Rightarrow (0.8 imes x) imes (y+10)= 100$$
$$Rightarrow (0.8x imes y)+(80 imes x)= 100$$
$$Rightarrow (80)+(80 imes x)= 100$$
$$Rightarrow (80 imes x)= 100-80 = 20$$
$$Rightarrow x= frac{20}{8} = 2.5$$/-
new price = $$0.8 imes x = 0.8 imes 2.5 = 2$$/- so the answer is option B.