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Question 3: High five

Fill in the blanks using +, -, *, or / to make this equation valid. You may also add parentheses if necessary.

5 _ 5 _ 5 _ 5 _ 5 = 24

Answer: Readers came up with a nice variety of answers to this question (see Solutions below). Very well done to: Simon Winfield, director, MacLellan Rubber Ltd, Wednesfield, Wolverhampton, UK; Kamila Staszewska, R&D / quality lead, Abcon Industrial Products Ltd, Cootehill, Co. Cavan, Ireland; Andrew Knox, Rubbond International, Ohé en Laak, The Netherlands; Kate Burns, senior technologist and regulatory officer, Prisma Colour Ltd, Birch Vale, High Peak, Derbyshire; Sabit Karayel, compound development manager,  Petlas Lastik Sanayi ve Ticaret A?, Türkiye; Michele Girardi, quality manager, Scame Mastaf SpA, Suisio, Italy; Semih Öngir, maintenance manager, Petlas Lastik Sanayi ve Ticaret A?, Türkiye.

An extra and exceptional well done to Michele Girardi, who cleverly deduced the answer to Q1 - one of our toughest ever teasers: The missing number is 47. The series is 29, 30, 50; 47; 47, 79.  Referring to sports and Olympics: The bronze medals are made of Copper, Tin and Zinc, whose atomic numbers are 29,30,50; the Silver medals are made of Silver whose atomic number is 47; and the Gold medals are made of Silver plated with Gold, whose atomic numbers are 47 and 79.

SOLUTIONS

Simon Winfield

5 x 5 x 5 – 5 / 5 = 24

5 x 5 x 5 = 125 – 5 = 120 / 5 = 24

Kamila Staszewska

The answer can be: (5 * 5 * 5 - 5) / 5 = 24

Andrew Knox

Answer: ((5*5*5)-5)/5=24

Dr Kate Burns

[(5*5*5)-5]/5

= (125 -5)/5

=120/5

=24

Sabit Karayel

((5*5*5)-5)/5=24

Michele Girardi

(5x5x5 -5 )/5 = 24

Semih Öngir

5*(5-(5/5)/5)=24

Fill in the missing years in this millennium sequence:

2307, 2417, 2527, 2637, _, _, _.

Answer: The rest of the sequence is: 2747, 2857, 2967 (add110), as neatly worked out by: Andrew Knox, Rubbond International, Ohé en Laak, The Netherlands; John Bowen, consultant, Bromsgrove, UK; Sabit Karayel, compound development manager, Petlas Lastik, Saniya ve Ticaret AS, Turkey; Michele Girardi, quality manager, Scame Mastaf SpA, Suisio, Italy; Sudi Sudarshan, principal consultant, Global Mobility Strategies, USA. Well done to all and everyone else who had a go.

(ps The new clue added to Q1 might help to reveal the answer)

Question 1: Tricky teaser

Complete the series

29, 30, 50; 47; ?, 79.

Clues: Sport, ----fish, Bronze...

Email your answer: correct replies next Friday*.

*As this teaser proved even trickier than we imagined, we'll run as a bonus question until we get a few correct answers - hopefully.