Hairu and the numbers part 11 (Math Question)

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To read  mathematics concept for Numbers go to posting Hairu and the numbers

Lower primary school mathematics question LPQ28

I am thinking of a 2-digit odd number. If I multiply it by 5, the answer is less than 140. If I multiply it by 4, the answer is more than 100. The sum of the 2 digits in the number is 9. What number am I thinking of?

Solution:

 

            First determine the range of the number,

 

            140 ÷ 5 = 28

 

            100 ÷ 4 = 25

 

            The number is either 26 or 27.

 

            Since it is an odd number and sum of the digits is 9, the number must be 27.

 

Alternative solution:

 

Using Guess and Check method

 

Digit in tens place

Digit in ones place (odd number)

Multiply by 5

Check < 140

Multiply by 4

Check > 100

4

5

225

×

180

2

7

135

108

 

                                The number is 27

 

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