A reduction of 21% in the price of wheat enables a person to buy 10.5 kg more for Rs. 100. What is the reduced price per kg?

Let original rate = Rs. P per kg
New rate = 79% of Rs. P per kg
= Rs. (79 x P)/100) per kg
∵ {(100/79P)/100} - {100/P} = 10.5
⇒ 10000/79P - 100/P = 10.5
⇒ 10000 - 7900 = 10.5 x 79P
∴ P = 2100/(10.5 x 79)
∴ P = 2100/(10.5 x 79)
Reduced rate = Rs. (79/100) x 2100/(10.5 x 79) per kg = Rs. 2 per kg.