If a sum of money amounts to ₹12,900 and ₹14,250

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If a sum of money amounts to ₹12,900 and ₹14,250 at the end of 4th year and 5th year respectively at a certain rate of simple interest, then the rate of interest is

SI = Amount - Principle
S.I. for 1 year = 14250 – 12900 = Rs. 1350
S.I. for 4 years = 1350 × 4 = ₹ 5400
∴ Principal = 12900 – 5400 = ₹ 7500

∴ Rate =	SI × 100
	Principal × Time

Rate =	5400 × 100
	7500 × 4

Rate = 18% per annum
Second method to solve this question :
Here , A₂ = ₹ 14250 , T₁ = 4 years , A₁ = ₹ 12900 , T₂ = 5 years

R =		A₁ - A₂		× 100
		A₂T₁ - A₁T₂

R =		12900 - 14250		× 100
		14250 × 4 - 12900 × 5

R =	- 1350	× 100
	57000 - 64500

R =	1350	× 100
	7500

R = 18%