5th Grade - Math

LESSON PROBLEM: Measurement: If you are asked when to start making rice cookies, which you have to complete by a certain hour on a particular date, how would you go about it?


STUDY GUIDE

Time holds a very important place in our lives. Our life is governed by time. We may not be conscious of this fact all of the time, but time is involved in anything we talk about or think of doing. Imagine, planting a certain number of acres of rice on a particular date and you want to plan for the time of harvest. Just in talking about one thing, planting rice, we have used the time factor several times, and we could have used it many more times. It is important for us to be able to keep track of time and to be able to manage it properly.

We divide time in units - big and small. In our daily activities, we measure time in a unit as small as a second, and as big as a year. In specialized fields like medicine, science, sports, and space technology even fractions of seconds are significant. In other fields like archeology and geology time is measured in millions of years. The rice farmer uses the growing season as a unit of measure.

Units of time:

1.Century - 100 years
2.Decade - 10 years
3.Year - 365 days
4.Year - 12 months
5.Year - 52 weeks
6.Month - 30 days
7.Week - 7 days
8.Day - 24 hours
9.Hour - 60 minutes
10.Minute - 60 seconds


Facts to remember when using measurement.


Read time accurately
When using a decimal system in units of measurement such as mass, money, and distance, remember that there are different fractions to define each unit.
When converting a day to an hour, remember there are 24 hours in a day.

Look at this example. You leave for school at 8:10 a.m. in the morning. Your mother needs 25 minutes to cook rice cereal for you, which should be ready by 8:00 a.m. At what time should she start cooking the cereal?

She should start cooking 25 minutes before 8:00 a.m. Subtract 25 minutes from 8 hours. Look at the results below:

HoursMinutes
800
025
735


How did we solve the problem. We could not subtract 25 from 00, so we borrowed one hour from 8. This left us with 7 hours and 60 minutes. The results are below:

HoursMinutes
800
760
025
735


Remember, one hour is 60 minutes. Subtract 25 from 60, to get 35. So your Mom should start cooking the rice cereal no later than 7:35 a.m.

Now try to do the following:

1.You have a one-hour lunch break at school. It takes you 18 minutes to eat your rice pilaf lunch. The rest of the time you play or chat with your
classmates. How many minutes can you chat or play with your classmates?
2.Your lunch break ends at 12:00 noon. If you want to save 20 minutes for fun, at what time should you finish your lunch?

Your grandmother makes rice dumplings, and it takes her 30 seconds to make one rice dumpling, how long would she need in order to make 100 rice dumplings for your birthday party?

To solve this problem, you have to first find out how many seconds she will need. Multiply the time taken for one dumpling, by the number of dumplings she will make for the birthday party. This is how to do it:

Time taken for one rice dumpling - 30 seconds
Time required for 100 rice dumplings - 30 x 100 = 3,000 seconds

It is awkward to work with thousands of seconds, so convert it to bigger units, minutes. To find the number of minutes, divide by 60. (1 minute = 60 seconds)

Divide 3,000 by 60, = 50. So, your grandmother needs 50 minutes to make 100 dumplings.

Now try the following:

1.It takes a restaurant five minutes to pack one meal of rice noodles. If they have 80 orders, how long will it take to pack the order?
2.Now, if the restaurant has to deliver the order at 7:00 in the evening, when should they start packing the order to be able to deliver it in time?


Your Dad buys a 10 kg bag of milled white rice on the 8th of the month. Your Mom cooks 250 grams of rice every day. When will she need another bag of rice, if she started using this bag of rice on the 8th of the month? (Assume that a month has 30 days.)

To solve this problem, find the number of days that the bag of rice will last. Divide 10 kg. by 250 grams. (250 gram = .25 kg.)

Divide 10 kg. by 250 grams. The results are:

Total number of days the rice would last = 10 / .25 = 40 days

Now find the date. The bag is started on the 8th. So, it will last 23 days of the current month, and 17 days of the next month. The new bag of rice will be needed on the 18th of the next month.

Do you know how we got 23? The bag of rice was started on the 8th, after 7 days of the month were over. So subtract 7 from 30, and get 23. But, the 10 kg. bag is enough for 40 days. Subtract 23 from 40, and get 17. The bag of rice will last for 17 days of the next month.

Now try the following:

1.You buy a box of 10 rice snacks. You eat one rice snack every day. If you started this box on the 5th, when would it be finished?
2.Your uncle gets you a big bag of 100 rice cookies. You share it with your sister, and together, the two of you eat two cookies each per day. If you
start this bag on the first of the month, when will it be finished?

When working with weeks, remember that there are 7 days in a week, 4 weeks in a month, and 52 weeks in a year. With the help of the units of time list
at the beginning, try the following:

1.A family eats 350 grams of rice each day. How much rice do they eat in a week?
2.Every month, Mr. Peter buys 12 kg. of long grain rice. How much rice does his family eat each week.?
3.Susan spends $55 on rice foods each month. How much does she spend each year on rice foods?
4.The annual income from the sale of rice products in a small store is $54,000. Find the store's monthly, weekly, and daily income.



ACTIVITIES

While enjoying a chat with your friends during lunch hour at school, try to find out how long it takes to cook the different rice dishes that your friends bring.
Then compare their times and calculate the difference of time over the period of a week, a month, and a year.



EXTENDED LEARNING

There are 30 days in a month, and there are 12 months in a year. This makes 30 x 12 = 360 days.

But there are 365 days in a normal year, and 366 days in a leap year. Try to find out how these 5-6 days are accounted for.


VOCABULARY
  • annual
  • reference
  • sufficient
  • assume
  • continuation
  • specialized
  • archeology
  • geology


Click here to play Rice Rampage!
How is Rice Grown:
Farming rice is hard work. Click here to learn more about the Stages of Farming Rice.
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