RRB Group-D Model Paper 12 with answers for online practice

Given:
Cost Price of phone = Rs. $\left(40{\mathit{x}}^2+20\mathit{x}\right)$
Selling Price of phone = Rs. $\left(60{\mathit{x}}^2+30\mathit{x}\right)$
Concept used:
Profit% = (SP – CP) / CP × 100
Solution:
Profit = SP – CP =$60{\mathit{x}}^2+30\mathit{x}\mathit{–}40{\mathit{x}}^2\mathit{–}20\mathit{x}$
⇒ Profit = $20{\mathit{x}}^2$ + 10x = 10x(2x + 1)
CP = 20x(2x + 1)
∴ Profit% = Profit / CP × 100
⇒ [10x(2x + 1) / 20x(2x + 1)] × 100
⇒ (10 / 20) × 100
⇒ 50%