1 · The two hands
The short hand tells the hour. The long hand tells the minutes. When the long hand points straight up at 12, it is exactly o'clock.
When the long hand points at 6, it is half past: 30 minutes. Notice the short hand has moved halfway between 3 and 4.
2 · Counting by fives
Each big number on the clock is 5 minutes for the long hand. Count around: 5, 10, 15, 20...
The long hand points at 4, so count 5, 10, 15, 20. The short hand is just past 7. The time is 7:20.
3 · To the minute
The small marks between the numbers are single minutes. Count by fives to the last big number, then count the small marks one at a time.
Long hand: past the 4 (20) by 3 small marks = 23. Short hand: past 7. The time is 7:23.
4 · a.m. and p.m.
The clock goes around twice a day. From midnight to noon is a.m. (morning). From noon to midnight is p.m. (afternoon and night).
7:30 a.m. is breakfast time. 7:30 p.m. is bedtime-story time. The clock looks the same, but one is morning and one is night.
5 · Elapsed time: hop along a number line
Elapsed time is how much time passed. Hop in easy pieces: whole hours first, then minutes.
Start at 2:40 and go 1 hour 20 minutes. Hop 1 hour to 3:40, then 20 minutes to 4:00.
6 · Finding the end time
Soccer starts at 1:45 and lasts 2 hours 45 minutes. Hop 2 hours: 3:45. Hop 15 minutes to the next hour: 4:00. Hop the last 30 minutes: 4:30.
Breaking the minutes at the hour keeps you from going past 60.
7 · How long did it take?
Now the start and end are known. From 9:15 to 11:05: hop to 10:15 (1 h), then 11:05 is 50 minutes more. Total 1 hour 50 minutes.
8 · Length: inches and centimeters
Line the object up with 0 on the ruler and read where it ends. This pencil is 5 inches long.
The small marks split each inch into halves and quarters, just like a line plot.
9 · When the object does not start at 0
Sometimes the object starts in the middle of the ruler. Then the number at its end is not its length. Count the spaces between its start and its end, or subtract: end minus start.
This ribbon starts at 3 and ends at 8. Its length is 8 − 3 = 5 centimeters, not 8. Test makers love this trap, so always check where the object starts.
The marks between the inch numbers are halves and quarters. A key that ends at the middle mark after 3 is 3½ inches long.
10 · Picking the right unit
Small things: inches or centimeters (a paper clip is about 3 cm). Medium things: feet or meters (a door is about 7 feet, or 2 meters). Long distances: miles or kilometers.
If the answer would be a huge number, pick a bigger unit.
11 · Weight: grams, kilograms, ounces, pounds
A paper clip weighs about 1 gram. A textbook weighs about 1 kilogram (1,000 grams). A slice of bread is about 1 ounce; a loaf is about 1 pound (16 ounces).
A balance tips toward the heavier side. 1 kilogram beats 500 grams.
12 · Liquids: milliliters and liters
A spoonful is about 5 milliliters. A big water bottle is 1 liter, which is 1,000 milliliters.
This jug is filled to 750 mL, three quarters of a liter.
13 · Reading a scale: what is each mark worth?
Thermometers, scales and measuring cups do not label every mark. Before you read one, find out what one mark is worth: take two numbers next to each other and count the jumps between them.
On this thermometer, 30 and 40 are 5 jumps apart. 10 ÷ 5 = 2, so each mark is 2 degrees. The liquid stops 3 marks above 40: 40, 42, 44, 46°F.
Some numbers to know: water freezes at 32°F (0°C). A warm summer day is about 80°F. Your body is about 98°F.
14 · Converting units
Some facts to keep in your pocket: 1 foot = 12 inches, 1 yard = 3 feet, 1 meter = 100 cm, 1 kilogram = 1,000 g, 1 liter = 1,000 mL, 1 hour = 60 minutes.
2 feet = 2 × 12 = 24 inches. 3 hours = 3 × 60 = 180 minutes.
15 · Comparing different units
Which is longer, 4 feet or 50 inches? You cannot compare 4 and 50, because they are different units. Change one so both use the same unit: 4 feet = 4 × 12 = 48 inches. Now 50 inches is longer.
Change the bigger unit into the smaller one. It is a multiplication, and you never need fractions.
16 · Calendars: days, weeks, months
7 days make a week, about 4 weeks make a month, and 12 months make a year. On a calendar, the day one week later is straight below.
March 4 is a Saturday. Two weeks later is two boxes down: 4 + 7 + 7 = March 18, also a Saturday.
17 · Same speed, longer trip
Nisha rides 3 miles in 18 minutes. At the same speed, how long does 12 miles take? 12 miles is 4 times as far, so 4 times as long: 4 × 18 = 72 minutes.
A map works the same way: if 1 inch stands for 20 miles, then 140 miles is 140 ÷ 20 = 7 inches. Find how many groups, then multiply.
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