# ERJ Brainteaser: July

4 Jul 2021

For some super-sharp answering, especially to Q4, the top award goes to **David Mann** of SPC Rubber** **Compounding, new holder of our **Brainiac of the Month** title

Find the connection between these numbers:

29 50, 47, 79

The gold medal goes to **David Mann**, key account manager, SPC Rubber Compounding, UK, who quickly came up with the correct answer, followed a bit later by: **John Bowen**, rubber industry consultant, Bromsgrove, Worcs, UK (silver); and **Andrew Knox**, Rubbond International, Ohé en Laak, The Netherlands (bronze). These top Brainiacs identified the link: these are the atomic numbers of the metals used in Olympic medals - currently being dished out in Tokyo. Well done to our podium trio and everyone else who had a go.

New teaser on Monday

Which number comes next in the following series?

11, 31, 71, 91, 32, _

**Answer**: This is series of prime numbers with the digits reversed, making the next number 92. Well done to: **David Mann**, key account manager, SPC Rubber Compounding, UK; **Andrew Knox**, Rubbond International, Ohé en Laak, The Netherlands; **Stephan Paischer**, head of product management special products, Semperit AG Holding, Vienna, Austria; **Michele Girardi**, Scame Mastaf Spa, Suisio, Italy; **Torsten Rupp**, sales EMEA, ContiBladders, Continental Reifen Deutschland GmbH, Division Tires, Hannover, Germany; **Michael Easton**, director, Globus Group, Trafford Park, Manchester, UK; **Flemming Vorbeck**, purchasing manager commercial, NDI Group A/S, Brørup, Denmark; **France Veillette**: chef environnement, Usine de Joliette, Bridgestone Canada Inc., Canada; **Jose Padron**, material development specialist, Waterville TG Inc. Waterville, Québec, Canada.

Solutions

*A few interesting takes on this week’s teaser:*

*Torsten Rupp*

*If you turn around the number you will get:
11; 13; 17; 19; 23
• If you alternately add 2 and 4 the following number will be 25 and the answer = 52
• But the numbers are all prime numbers as well. The following one is 29 and the answer = 92.
• Surprisingly also 24 can be correct, because the answer to life, the universe and everything = 42*

*Andrew Knox*

*This is a series of prime numbers (luckily in base 10!) with the digits reversed. Clue: Series don’t usually go down, but here the second digit does go up slowly…*

*Jose Padron*

*(Many thanks for the funny cartoon – but, yes, we do need to check the copyrights...).*

New teaser on Monday

The traffic lights turn green and a car immediately starts from stationary. The car accelerates at a constant rate of 6 m/s². A bus passes the traffic lights just as they turn green. The bus is travelling at a constant speed of 18 m/s. How many seconds does it take for the car to overtake the bus?

**Answer**: First a big well done to David Mann, Andrew Knox and John Bowen for providing the correct answer to the High five! question (see below) early last week, without any clues. This week’s teaser also proved quite tough, with just a select few working out the correct answer at 6 seconds (solutions below). So, very done also to: **Michele Girardi**, Scame Mastaf Spa, Suisio, Italy; **Stephan Paischer**, head of product management special products, Semperit AG Holding, Vienna, Austria; **Andrew Knox**, Rubbond International, Ohé en Laak, The Netherlands; **John Rollins**, Delta-Energy Group, LLC Natchez, Mississippi, USA: **France Veillette**: chef environnement, Usine de Joliette, Bridgestone Canada Inc., Canada; and everyone else who had a go.

Solutions

*Michele Girardi
The equation of motion of the bus is x=v*t
- the one of the car is x=1/2*a*t^2
when the car starts overtaking the bus it's
v*t=1/2*a*t^2
t=v/(1/2*a) = 2*18/6s = 6s
(To calculate when the overtaking is over you need to know the length of the car…)*

*Stephan Paischer
Bus: in six seconds, it has travelled 108 m (6 x 18 m/s).
Car: in six seconds, it has accelerated to 36 m/s2, and an average speed of 18 m/s (half of it; so a travelled distance of 6 x 18 m/s = 108 m).*

*Andrew Knox
Distance travelled by bus = velocity x time or v.t
Distance travelled by car is 1/2 (acceleration x time ^2) or 1/2.a.t^2
So, distance is same when v.t = 1/2.a.t^2 or t = 6.
At this moment both the car and the bus have travelled 18 x 6 = 108 metres. *

*France Veillette
They will meet at same distance from light, so d=speed*time and d=1/2 acc*time2, therefore time=2*18/6 or 6 seconds.*

Bonus question: **High five**

If 5+5 equals 14, what does 5 x 5 equal?

(Results carried over from last week)

Great play by **David Mann**, key account manager, SPC Rubber Compounding, UK; **Andrew Knox**, Rubbond International, Ohé en Laak, The Netherlands: and **John Bowen**, rubber industry consultant, Bromsgrove, Worcs, UK, who quickly spotted that these numbers were to the base 6, making the answer 41 (four 6s plus 1). Well done also to: **Jose Padron**, material development specialist, Waterville TG Inc. Waterville, Québec, Canada; **Michele Girardi**, Scame Mastaf Spa, Suisio, Italy; **Stephan Paischer**, head of product management special products, Semperit AG Holding, Vienna, Austria; **France Veillette**: chef environnement, Usine de Joliette, Bridgestone Canada Inc., Canada; and everyone else who took on this tricky challenge.

New teaser on Monday.

.

If 5+5 equals 14, what does 5 x 5 equal?

**Answer**: There were a couple of correct replies (you know who are!) but this teaser proved much trickier than expected. So, we have decided to roll it over as a bonus question next week – adding a clue to two...