1st Class Mathematics Back & Forth Counting Counting in Twenties

   Counting in Twenties  

Look at the following:

One twenty           = 1 twenty =

Two twenties         = 2 twenties =

Three twenties      = 3 twenties =

Five twenties         = 5 twenties =

Twelve twenties     = 12 twenties =  

Now, it is clear that

One twenty is one fold of

Two twenties is twofold of

Three twenties is three fold of

Five twenties is fivefold of

Twelve twenties is twelve fold of  

Trick:

While counting in twenties, just double the number of times the twenty to be counted and put it in the left side, the word twenty/twenties written in the right side will be replaced by a single zero (0).  

(A)

Here, we double the two that becomesand put it in the left while the word twenties written in the right get replaced by zero (0).

(B)

Here, we double the five that becomesand put it in the left while the word twenties written in the right side get replaced by zero (0). Clearly counting in 20's goes as: 20, 40, 60, 80, 100, 120 ..........and so on.   

 Four twenties

(a) 140                                                 

(b) 80

(c) 40                                                    

(d) 60  

Answer: (b)  

Explanation

4 twenties is four fold of 20 = 80.

It is clear from the following diagram:

Option (A) is incorrect because it is clear from the following diagram that 140 is equal to seven twenties:

Option (C) is incorrect because it is clear from the following diagram that 40 is equal to two twenties:

Option (D) is incorrect because it is clear from the following diagram that 60 is equal to three twenties:

 Counting in twenties is given below. Fill the blank box with suitable number.  

(a) 160                                                 

(b) 180

(c) 200                                                  

(d) 60  

Answer: (a)  

Explanation

Here, we have to find the value of 8th box. It means that we need the value of eight twenties which is eight fold of 20 and eight fold of 20 is equal to 160. It is clear from the following diagram:

Option (b) is incorrect because 180 = Nine twenties that is clear from the following diagram:  

Option (c) is incorrect because 200 = 10 twenties that is clear from the following diagram:

Option (d) is incorrect because 60 = three twenties that is clear from the following diagram: