a man purchased some eggs at 3 for rs 5 and sold them at 5 for rs12 thus , he gained rs 143 in all  how many eggs did he purchased.

 Let the eggs he purchased be x

CP = 3 eggs ---- Rs 5

1 egg = 5 / 3 Rs

x eggs = 5x/ 3 Rs = 25x / 15

SP = 5 eggs ----- Rs 12

1 egg = 12 / 5 Rs

x eggs = 12x /5 Rs = 36x / 15

Comparing CP and SP we get SP > CP

Then it is a profit

Profit = 36x / 15 - 25x / 15 = 9x / 15

It is given he gained Rs 143

SP - CP = Gain

9x / 15 = 143

x = 143  * 15 / 9

x = 233.3333

Ans: approximately he bought 233 eggs

Sorry it is x = 238.3333333

he bought = 238 eggs

CP OF 3 EGGS=5Rs

CP OF 1 EGG=53Rs

SP OF 5 EGGS =12Rs

SP OF 1 EGG = 125Rs

NOW GAIN FOR 1 EGG=125-53=1115  (BY TAKING 15 AS LCM)

THEREFORE HE GAINS 1115Rs WHEN HE BUYS ONE EGG

SO HE WILL GAIN 1RUPEE ON BUYING 1511 EGGS  (BY UNITARY METHOD)

SO IF HE GAINS 143 Rs THE No. OF EGGS BROUGHT=143*1511= 195 EGGS ANS.

THIS ANSWER IS 100% CORRECT.

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 THIS ANS IS WRONG AND THE CORRECT ANS IS 195 EGGS

 CP OF 3 EGGS=5Rs

CP OF 1 EGG=5 / 3Rs

SP OF 5 EGGS=12Rs

SP OF I EGG=12 / 5Rs

NOW GAIN FOR 1 EGG=(12 / 5)-(5 / 3)=11 / 15  (BY TAKING 15 AS LCM)

THEREFORE HE GAINS 11 / 15Rs WHEN HE BUYS 1 EGG

SO HE WILL GAIN 1 RUPEE ON BUYING 15 / 11EGGS   ( BY UNITARY METHOD)

SO IF HE GAINS 143 Rs THE NO. OF EGGS BROUGHT=143*(15 / 11)=195 EGGS