Let cost price of whole be Rs x
Cost price of 1 / 4 th =Rs x/4
Cost price of 3 / 4 th = Rs 3x/4
Total selling price = Rs [(110% of x/4)+3x/4)]
= Rs [(110/100 * x/4) + 3x/4]
= Rs [11x/40 + 3x/4]
= Rs (11x+30x/40)
= Rs 41x/40
Gain = Rs 41x/40 – x = x/40
Gain % = x/40 * 100 *1/x = 100/40
Gain % = 2.5%