Think you have sharp eyes? Here’s a fun challenge for you! Hidden among a sea of number 5s is a sneaky little number 3—can you spot it? This optical illusion is a real test of your observation skills.

So you need to break it down further and think about the Roman numerals you can choose from. 70 can be partitioned into 50 and two 10s. 7 can be partitioned further into 5 and two 1s. These values ...