Counting By Fives

Counting by fives means adding five to previous number or jump by 5. Each number is 5 more than the previous number. if the 1st number is an odd number then the next number by adding 5 will be an even number. And if the 1st number is an even number then the next number will be an odd number. So counting by five's gives you alternatively odd and even numbers.

Example: Counting by 5's

If the 1st number is 8 then next 5 numbers obtained by counting by 5's are; 8, 8 + 5 =13; 13 + 5 =18; 18 + 5 =23; 23 + 5 = 28; 28 + 5 =33

So next 5 numbers after 8 are 13,18,23,28,33.

Example 1 : Find the next 3 numbers after 21 by counting it by 5's.

Solution : 1st number = 21 + 5 = 26

2nd number = 26 + 5 = 31

3rd number = 31 + 5 = 36

So next 3 numbers after 21 are : 26,31,36.

Example 2 : Find the missing numbers. 15,20,____,____,____,____.

Solution : 1st number is 15 and next number is 20 so from this we can see that its counting by 5's 

. That means after adding 5 to previous number we will get the next number. So,

1st missing number = 20 + 5 =25

2nd missing number = 25 + 5 = 30

3rd missing number = 30 + 5 = 35

4th missing number = 35 + 5 = 40

So the number are 15,20,25,30,35,40.

Example 3 : Complete the following pattern.

12,17,22,____,____,____

Solution : In 12,17 and 22 the gap of 5. That means by adding 5 we get a next number. So, 1st missing number is 22 + 5 = 27, 2nd missing number is 27 + 5 =32 and 3rd missing number is 32 + 5 = 37. Series is 12,17,22,27,32,37.

Practice

Q.1 Find the missing numbers.

1) 27,32,___,___,___,___,___,62

2) 61,66,___,___,81,___,___,

3) 51,___,61,65,___,___,___,

4) 84,___, 94,99,___

5) ,___,20,25,___,35,___