DAY 20:

Today’s Challenge

Consider all whole numbers from 1 through to 60 when deleting the following numbers:

  •  all prime numbers and square numbers,
  •  any number that differs by 1 from a prime or square,
  •  all multiples of 5,
  •  any number that differs by 1 from a multiple of 5,
  •  all multiples of 7,
  •  any number that differs by 1 from a multiple of 7.

One number should be left, what is it?

.

The 7puzzle Challenge

The playing board of the 7puzzle game is a 7-by-7 grid containing 49 different numbers, ranging from up to 84.

The 1st & 7th rows of the playing board contain the following fourteen numbers:

2     4     9     11     14     15     22     24     27     30     40     70     72     77

What is the difference between the highest prime number and highest square number?

Make 20 Challenge

Can you arrive at 20 by inserting 1, 4, 6 and 8 into the gaps on each line?

  •  (◯–◯)×(◯–◯) = 20
  •  (◯÷◯+◯)×◯ = 20
  •  (◯+◯)×◯–◯ = 20

Answers can be found here.

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