word problem

Question

Thomasita was thinking of a number less than 90 that she says when counting by sixes and when counting by fives, but not when counting by fours. Of what number was she thinking?

Answer 1

Multiples of 6 up to 90  or less than= 6,12,18,24,30,36,42,48,54,60,66,72,78,84

 

 

Multiples of 5 up to 90  or less than = 5,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80,85

 

Common multiples are  = 30,60

 

In this 2 numbers  60 is multiple of 4  but 30 is not multiple of 4

 

So she must be thinking about 30