Let CP of the watch be ₹ N.
Then , According to the question,
[(75 - N)/ N] x 100 = N

Correct Option: C

Let CP of the watch be ₹ N.
Then , According to the question,
[(75 - N)/ N] x 100 = N
⇒ (75 - N) x 100 = N²
⇒ N² + 100N - 7500 = 0
⇒ N² + 150N - 50N - 7500 = 0
⇒ N(N + 150) - 50 (N + 150) = 0
⇒ (N + 150) (N - 50) = 0
⇒ N = ₹ 50

Let each lot of onion-contain N kg onion,
Then total cost price of these two lots together = 10N + 15N = 25N
Selling price of whole lot = 15 x (N + N) = 15 x 2N = 30N

Correct Option: C

Let each lot of onion-contain N kg onion,
Then total cost price of these two lots together = 10N + 15N = 25N
Selling price of whole lot = 15 x (N + N) = 15 x 2N = 30N
Profit percentage = [(30N - 25N)/25N] x 100 %
= (5/25) x 100%
= 20%

Here, a = 10% and b = 20%
According to the formula,
Required answer= [b ± a/(100 - b)] x 100 %

Correct Option: D

Here, a = 10% and b = 20%
According to the formula,
Required answer= [b ± a/(100 - b)] x 100 %
= (20 - 10)/(100 - 20 ) x 100%
= (10/80) x 100% = 12.5 % gain
+ ve sign show that profit is earned here.

(SP of 100 pens) - (CP of 100 pens) = SP of 40 pens
⇒ SP of 60 pens = CP of 100 pens.

Correct Option: E

(SP of 100 pens) - (CP of 100 pens) = SP of 40 pens
⇒ SP of 60 pens = CP of 100 pens.

Let CP of each pen = ₹ 1
Then, CP of 60 pens = ₹ 60
SP of 60 pens = ₹ 100

Gain = 100 - 60 = ₹ 40
∴ Gain % = (40/60) x 100 % = 66.67%

Here, a = 16, b = 12
According to the formula,
Required gain percent = [(a - b)/b] x 100

Correct Option: A

Here, a = 16, b = 12
According to the formula,
Required gain percent = [(a - b)/b] x 100
= [(16 - 12)/12] x 100
= (4/12) x 100
= 33¹/₃% (gain)