Fac-Finding

Lyndon chose this as one of his favourite problems. It is accessible but needs some careful analysis of what is included and what is not. A systematic approach is really helpful.
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative


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Fac-Finding



If factorial $100$ ($100!$) was rewritten as the product of its prime factors how many $2$s and how many $5$s would there be?

 
Along the way, confirm how many zeros are at the end of this large number and what the first digit to precede them is.

In the Teachers' Resources, Lyndon explains why he likes this problem.