Every time you buy a snack, save your allowance, or check what time recess starts, you are using math. In this chapter you will learn the value of each coin, count money, and read both analog and digital clocks. Let’s get started!
1. Meet the coins
In the United States, money is counted in dollars and cents. The symbol for cents is ¢. You will see four coins most often.
A penny is worth 1¢. A nickel is worth 5¢. A dime is worth 10¢. A quarter is worth 25¢.
A dime is smaller than a penny and a nickel, but it is worth more than both. Always read the value, never judge by size.
2. Counting mixed coins
When you have different coins, counting is easier if you follow a plan. Sort the coins, put the biggest value first, and keep a running total.
- Sort the coins from the greatest value to the least value.
- Count the quarters by 25s, the dimes by 10s, and the nickels by 5s.
- Count the pennies by 1s.
- Say the total out loud and write it with the cent sign.
You have 1 quarter, 2 dimes, 1 nickel, and 2 pennies. Count: 25, 35, 45, 50, 51, 52.
\(25 + 10 + 10 + 5 + 1 + 1 = 52\). The coins are worth 52¢.
You have 3 nickels and 4 dimes. Start with the dimes: 10, 20, 30, 40. Then count the nickels by 5s: 45, 50, 55. The total is 55¢.
Zyro, the alien explorer, says: “On my planet we count stones, but on Earth you can count coins by skip counting. Say 25, 50, 75 for quarters and 10, 20, 30 for dimes!”
3. Dollar bills and cents
A dollar is worth 100 cents. A dollar bill, four quarters, ten dimes, and one hundred pennies all make the same amount.
\(1\text{ dollar} = 100\text{ cents}\). We write money with a dollar sign and a decimal point. The decimal point separates the dollars from the cents.
You have 135¢. Think: \(135 = 100 + 35\). That is 1 dollar and 35 cents, which we write $1.35.
Bigger bills help us count faster. A $5 bill is worth 5 dollars, and a $10 bill is worth 10 dollars. So 2 five-dollar bills and 1 one-dollar bill make $11.
If you have 2 dollars and 7 cents, write $2.07, not $2.7. There must always be two digits after the decimal point.
4. Money word problems
In a money word problem you add to find a total, or you subtract to find how much is left or how much change you get. Change is the money the cashier gives back when you pay with more than the price.
- Read the problem and find the numbers.
- Decide: do I put amounts together (add) or take away (subtract)?
- Solve, then check that the answer makes sense.
- Write a sentence with the unit: ¢ or $.
Noah buys an eraser for 35¢ and a pencil for 45¢. How much does he spend?
\(35 + 45 = 80\). Noah spends 80¢.
Noah pays with a one-dollar bill. How much change does he get?
\(100 - 80 = 20\). Noah gets 20¢ in change.
5. Reading an analog clock
An analog clock has a round face with the numbers 1 to 12 and two hands. The short hand is the hour hand. The long hand is the minute hand. There are 60 minutes in 1 hour.
When the minute hand points straight up at the 12, it is an o’clock time. If the hour hand points to the 4, the time is 4:00, or four o’clock.
6. Telling time to five minutes
The minute hand moves around the whole clock in 60 minutes. Each number on the clock stands for 5 minutes, so you count by 5s as you go around.
| Minute hand on | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Minutes after the hour | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 | 0 |
When the minute hand is on the 3, it is quarter past the hour (15 minutes). When it is on the 6, it is half past the hour (30 minutes). When it is on the 9, it is 45 minutes after the hour.
The hour hand is between the 8 and the 9, and the minute hand points to the 8. Count by 5s to the 8: 5, 10, 15, 20, 25, 30, 35, 40. The time is 8:40.
Look at the hour hand carefully. It has not reached the next number yet, so you use the smaller hour. At 8:40 the hour is still 8.
7. Analog and digital clocks
A digital clock shows the time with numbers. The number before the colon is the hour. The two numbers after the colon are the minutes.
A digital clock shows 6:45. On an analog clock, the minute hand points to the 9 because \(9 \times 5 = 45\). The hour hand is almost at the 7, but the hour is still 6.
Five minutes after three is written 3:05, not 3:5. The minutes always use two digits.
8. a.m. and p.m.
A day has 24 hours, but a clock face shows only 12 of them. The clock goes around twice every day. We use a.m. and p.m. to tell the two trips apart.
a.m. means the time from midnight to just before noon. p.m. means the time from noon to just before midnight.
Eating breakfast at 7:30 a.m. happens in the morning. Eating dinner at 6:00 p.m. happens in the evening. Noon is 12:00 p.m., and midnight is 12:00 a.m.
Key takeaways
- Penny = 1¢, nickel = 5¢, dime = 10¢, quarter = 25¢.
- To count mixed coins, start with the greatest value and skip count.
- 100¢ = $1. Write money with a decimal point, such as $1.35 or $2.07.
- In a word problem, add to find a total and subtract to find change.
- The short hand shows the hour. The long hand shows the minutes.
- Each number on the clock is 5 minutes more: count by 5s.
- a.m. is from midnight to noon. p.m. is from noon to midnight.
Test yourself: quick challenge for Grade 2
Speed drill for Grade 2: how many in 60 seconds?
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