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A vendor sells lemons at the rate of 5 for $ 14, gaining thereby 40%. For how much did he buy a dozen lemons?
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- $ 20
- $ 21
- $ 24
- $ 28
Correct Option: C
Given that , S.P. of 5 lemons = $ 14
On gain 40% ,
| C.P. of 5 lemons = | × 14 = $ 10 | 140 |
| ∴ C.P. of 12 lemons = | × 21 = $ 24 | 5 |
We can find required answer with the help of given formula :
Here, a = 12, p = ? and b = 5, q = 14, Gain% = 40%
| Gain% = |  | aq - bp |  | × 100% | |
| bp |
| 40% = | | 12 × 14 - 5 × p | | × 100% | |
| 5p |
⇒ 2p = 168 – 5p
⇒ 7p = 168
⇒ p = 24
