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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