Question

Dr ew does push ups every three days starting on January 3. He does sit-ups every four days starting on january 4, On which days in January will he do both push-ups and sit-ups? Use words numbers, or models to justify your answer.

Answer 1

Here is a thought:
list the dates he does push-ups,
3 6 9 12 ...
list the dates he does sit-ups,
4 8 12 ...
well guess what?

Here is another thought:
What is the LCM of 3 and 4 ?
On which days in January will this happen again?