GoalReview arrays, multiplication and division facts, fact families and reading time on clocks.
New words
array · things in equal rows and equal columnsfact family · multiplication and division equations that use the same three numberselapsed time · the time that passes between two clock times
Explanation
Multiplication means equal groups. An array with 4 rows of 6 has 4 × 6 = 24 items. Swapping the factors gives the same product: 6 × 4 = 24. Division is the opposite: 24 ÷ 4 = 6 and 24 ÷ 6 = 4. The numbers 4, 6 and 24 make a fact family. Multiples of 10 are easy: 6 × 70 = (6 × 7) × 10 = 420. On an analog clock the minute hand points to 1 for 5 minutes, to 2 for 10 minutes, to 3 for 15 minutes, and so on. A digital clock shows the hours and the minutes, like 3:45. Twenty-five minutes later it is 4:10.
Worked examples
The fact triangle has 40 at the top and 8 and 5 at the bottom. The fact family is 8 × 5 = 40, 5 × 8 = 40, 40 ÷ 8 = 5 and 40 ÷ 5 = 8.
The minute hand points at 9, and 9 × 5 = 45 minutes. The hour hand is between 3 and 4. The time is 3:45. Add 15 minutes to reach 4:00, and 10 more to reach 4:10, so 25 minutes later it is 4:10.
Hana shares 36 guavas equally among 9 baskets. 36 ÷ 9 = 4 guavas in each basket. Check: 9 × 4 = 36.
Class activity
Fact family cards. Make fact triangles for 7, 8 and 56, for 6, 9 and 54 and for 4, 12 and 48. Cover one number and ask a partner to find it. Then say the four equations of each family. Finish with a clock game: set a time on a clock, say how many minutes later it is, and ask your partner for the new time.
Practice
1
What time does the clock show? What time is it 35 minutes later?
The minute hand points at 4, which is 20 minutes, so it is 8:20. Thirty-five minutes later: 8:20 + 35 minutes = 8:55.
2
Find the missing factor: ? × 7 = 56.
8, because 56 ÷ 7 = 8.
3
Write the four equations of the fact family for 6, 9 and 54.
