14
Divisibility rule for 5
Textbook: Part 1, lesson 14, pp. 43–45
GoalKnow the divisibility rule for 5; convenient ways to multiply with 5.
New words
multiple of 5 · 5 ga karralilast digit · oxirgi raqamconvenient multiplication · qulay ko‘paytirishproduct · ko‘paytma
Explanation
Divisibility rule for 5: a number that ends in 0 or 5 is divisible by 5. Every number divisible by 10 is also divisible by 5, but not the other way round (35 is divisible by 5 but not by 10). Remember these handy products: 2 × 5 = 10, 4 × 25 = 100, 8 × 125 = 1 000. They make multiplying easier.
Worked examples
2 × 43 × 5 = 43 × (2 × 5) = 43 × 10 = 430.
125 × 6 × 8 = (125 × 8) × 6 = 1 000 × 6 = 6 000.
Class activity
“Find the pair”: cards show 2, 5, 4, 25, 8, 125. Children find pairs whose product is 10, 100 or 1 000.
Practice
1
From 15, 22, 40, 51, 105, 3 998, 7 775 write those divisible by 5.
15, 40, 105, 7 775
2
Calculate 25 × 17 × 4 conveniently.
1700
3
Calculate 8 × 39 × 125 conveniently.
39000
4
Which digits can replace the star so that 38* is divisible by 5?
0 or 5