Page 113 - ICSE Math 8

12x 3x Ê 3 xˆ 28 x
∴ New profit = 12% of x = ` = ` ⇒ New S.P. = ` x + ˜ = `
Á
100 25 Ë 25 ¯ 25
According to the question, the difference between new S.P. and original S.P. is ` 25.
28 11x 56x − 55x x
⇒ x – = 25 ⇒ = 25 ⇒ = 25 ⇒ x = 50 × 25 = 1,250
25 10 50 50
Hence, the C.P. of CD player = ` 1,250

Example 5: By selling 33 oranges, a fruit seller gains the selling price of 11 oranges. Find the profit per
cent.
Solution: Profit = S.P. of 33 oranges – C.P. of 33 oranges
⇒ S.P. of 11 oranges = S.P. of 33 oranges – C.P. of 33 oranges
⇒ C.P. of 33 oranges = S.P. of 33 oranges – S.P. of 11 oranges
⇒ C.P. of 33 oranges = S.P. of 22 oranges
Let the C.P. of 1 orange = ` 1

∴ C.P. of 33 oranges = ` 33 = S.P. of 22 oranges
⇒ S.P. of 22 oranges = ` 33
33 3
⇒ S.P. of 1 orange = ` = `
22 2
Ê 3 ˆ 1
Profit = S.P. of 1 orange – C.P. of 1 orange = ` Á Ë 2 - 1 ˜ = ` 2
¯
1
Profit 2 1
∴ Profit % = × 100 = × 100 = × 100 = 50%
C.P. 1 2
∴ Profit % = 50%
Example 6: Honey sold a wrist watch to Kirti at 20% profit. Kirti further sold it to Muskan at a profit of
5%. If Muskan paid ` 441 for it, what was the cost price of the wrist watch?

Solution: Let the cost price of the wrist watch be ` x.
Honey’s profit% = 20%
Ê 100 + Profit%ˆ Ê 100 20+ ˆ 120 6
S.P. for Honey = Á Ë 100 ˜ ¯ C.P.¥ = ` Á Ë 100 ˜ ¯ ¥ x = ` 100 x = ` 5 x

6
S.P. for Honey = C.P. for Kirti = ` x
5
Kirti’s profit = 5%

Ê 100 + Profit%ˆ Ê 100 5+ ˆ 6 Ê 105 6 ˆ 126
∴ S.P. for Kirti = Á 100 ˜ ¯ C.P.¥ = ` Á Ë 100 ¯ ˜ ¥ 5 x = ` Á Ë 100 ¥ x = ` 100 x
˜
5 ¯
Ë
S.P. for Kirti = C.P. for Muskan
126x 441 100×
⇒ = 441 ⇒ x = = 350
100 126
Hence, C.P. of the wrist watch = ` 350

Example 7: Anuradha purchased some buttons at 3 for ` 5 and sold them at 5 for ` 12. She gained ` 143
in all. How many buttons did she purchase?
Solution: Let the number of buttons purchased by Anuradha be x.
C.P. of 3 buttons = ` 5

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