Illustrative Example 3. Find the interest on $1800 for 3 years, 6 months, 16 days at 3%.

Note. The months should be divided up so that either 1 month's or 2 months' interest appears in the work in order that the number of days may be broken up so that they are an aliquot part of either 1 or 2 months.

This leads to the following rule:

1. Multiply the principal by the rate of interest. Multiply this result by the number of years if there is more than one year.

2. Change the number of months into aliquot parts of one year. By the use of these aliquot parts find the interest for the number of months required.

3. Change the number of days (if necessary) into aliquot parts of 30 days or of 60 days.

4. Find the interest for the required number of days.

5. Find the total interest.

Do-It-in-Your-Head Practice

1. What is the interest on $100 for 1 year at 6%? for 2 years? for 5 years?

2. 6 months is what part of 1 year?

3. How much would be the interest on $100 for 6 months at 6%?

4. What part of a year is 3 months? 4 months? 1 month?

5. What part of 1 month is 5 days? 6 days? 15 days? 10 days? 2 days? 1 day?

I. R. B. Test [1]. A Standard Time (for your class) to do the work of this and the other tests of this chapter should be fixed by your Steering Committee and Teacher (ex officio) when you take the First Trials. Prepare the I. R. B. Chart for Chapter X (7 tests). Enter your First Trial scores for [1].

Do-It-in-Your-Head Plus Paper-and-Pencil
Practice in Interest

Solve the following ten problems.

1. Find the interest on $840 for 5 years at 6%.

2. What is the interest on $1020 for 3 years at 5%?

3. Find the interest on $320.50 for 2 years at 8%.

4. What is the interest on $1650 for 2 years, 6 months at 6%?

5. Find the interest on $1280 for 3 years, 4 months at 6%. What is the amount? See page 248.

6. What is the interest on $150 for 6 years, 2 months at 6%?

7. Find the interest on $2530 for 3 years, 8 months at 5%. What is the amount?

8. What is the interest on $1600 for 4 years, 9 months, 15 days at 6%?

9. Find the interest on $3600 for 2 years, 5 months, 16 days at 5%.

10. Principal $4800, time 3 years, 10 months, 23 days. Rate 6%. Find the interest,

Finding the Time between Two Dates. To find the time between two dates we subtract the earlier date from the later. In order to do this we must know the number of each month as shown in the following table at the right.

Illustrative Example 1. Find the time between March 10, 1926, and August 16, 1927.

Solution: March is the 3d month and

August is the 8th month.

1. January

2. February 3. March

4. April

5. May

6. June

Hence the time is 1 year, 5 months, 6 days.

11. November

12. December

Illustrative Example 2. Find the time between November

12, 1921, and September 6, 1927.

Explanation: We cannot take 12 days from 6 days, so we borrow a whole month from 9, leaving 8. Thus we have 36 days from which to take 12 days. This leaves 24 days.

We cannot take 11 months from 8 months, so we borrow a whole year, leaving 1926. The year that we borrowed consists of 12 months. Thus we have 20 months from which to take 11 months, leaving 9 months. Subtracting 1921 from 1926 we have 5 years. Hence the time is 5 years, 9 months, 24 days.

Illustrative Example 3. Find the exact number of days from June 12, 1927 to September 21, 1927.

Solution:

18 days left in June

31 days in July

31 days in August

21 days in September

101 days from June 12 to September 21

Oral Test

1. How many actual days from March 5 to March 20? 2. How many actual days from June 20 to July 10?

3. What is the exact number of days from September 15 to October 20?

4. Find the number of actual days from February 12 to March 15, in a leap year.

I. R. B. Test [2]. Enter First Trial scores. In this exercise ask no help of any one. Work the 16 examples by yourself in any way you choose until you have a 100% record. Stick to it even if you are obliged to work overtime. Remember “A winner never quits and a quitter never wins.” Find the time between the following dates:

1. August 8, 1923 and November 18, 1927. 2. March 5, 1921 and October 15, 1927.

3. From Peary's discovery of the pole April 6, 1909 to Byrd's flight over the pole May 9, 1926.

4. From the signing of the Declaration of Independence July 4, 1776, to the "Sesqui" celebration of it in Philadelphia July 4, 1926.

5. From the beginning of regular air mail service between New York and San Francisco, July 1, 1924, to today.

6. From the beginning of the World War, August 3, 1914, to the end, November 11, 1918.

7. From the battle of Bull Run, July 21, 1861, to the battle of Gettysburg, July 1, 1863.

8. From the start of the round-the-world flight, March 17, 1924, to its end, September 9, 1924.

9. Abraham Lincoln was born Feb. 12, 1809, and died April 15, 1865. How long did he live?

10. Find the interest on $440 from January 10, 1923 to August 20, 1927 at 6%.

11. What is the interest on $680 for the exact number of days from June 6 to August 5 at 6%?

12. Find the interest on $1820 from September 3, 1924 to November 18, 1927 at 5%.

13. How much interest will pay for a loan of $1200 from October 5 to November 4 at 6%? How much will pay the whole indebtedness? (Amount prin. + int.)

=

14. Mr. Henry borrowed $12,000 on March 6 and repaid it on May 5 at 6% interest. How much did he owe at that time?