The formula is given below :

S.I x 100

Rate % = R = -------------

P x T

Amount = A = P + S.I

1) P = $ 20,000 Amount = $ 21,800 and time T = 2 years. Find the rate.

Amount = P + S.I

21,800 = 20,000 + S.I

S.I = 21,800 - 20,000

S.I = $ 1,800

S.I x 100

Rate % = R = -------------

P x T

1800 x 100

Rate % = R = -------------

20,000 x 2

180,000

Rate % = R = -------------

40,000

Rate = 4.5%

_______________________________________________________________

2) P = $ 625 Amount = $ 641.25 and time T = 146 days. Find the rate.

Amount = P + S.I

641.25 = 625 + S.I

S.I =641.25 - 625

S.I = $ 16.25

S.I x 100

Rate % = R = -------------

P x T

As the rate is given in days so T = 146 days = 146/365 =0.4 years

16.25 x 100

Rate % = R = -------------

625 x 0.4

1625

Rate % = R = -------------

250

Rate = 6.5%

______________________________________________________________

3) At what rate percent will a sum of money treble itself in 12 years?

A = 3P

t = 12 years

A = P + I

But I = PRT/100

∴ A = P - (PRT/100)

3P = P - (PRx12/100)

3P- P = 12PRT/100

2P = (12 x P x R)/100

cross multiply

2P x 100 = 12 PR

200P = 12 PR

R = 200P/12P

∴ R = 200/12

∴ R = 50/3 % = 16.66%

• Finding rate when Principal and time are given

• Finding time when Principal and rate are given

• Solved examples on Simple Interest

GMAT

GRE

1st Grade

2nd Grade

3rd Grade

4th Grade

5th Grade

6th Grade

7th grade math

8th grade math

9th grade math

10th grade math

11th grade math

12th grade math

Precalculus

Worksheets

Chapter wise Test

MCQ's

Math Dictionary

Graph Dictionary

Multiplicative tables

Math Teasers

NTSE

Chinese Numbers

CBSE Sample Papers