MATHS PROBLEM

Each week, Mr Tuckwell is giving our staff a fun maths problem to solve. I’ve shared our latest two problems with you. See if you can find the answer.

PROBLEM ONE

Place plus (+) and / or minus (-) signs in between the digits    1 2 3 4 5 6 7 8 9    so that the answer becomes 100.

For example

12 + 34 + 5 + 6 7 - 8 – 9 = 101. Close but not the right answer

123 + 4 + 5 – 6 – 7 – 8 – 9 = 102   Close but not the right answer!

Note:   There is more than one possible answer.  

Can you also find an answer using only 3 operations?

1  2  3  4  5  6  7  8  9 = 100

PROBLEM 2

Four people come to a river in the night. There is a narrow bridge, but it can only hold a maximum of two people at a time. They have one torch and, because it's night, the torch has to be used when crossing the bridge.

Person A can cross the bridge in 1 minute.

Person B can cross the bridge in 2 minutes.

Person C can cross the bridge in 5 minutes.

Person D can cross the bridge in 8 minutes.

When two people cross the bridge together, they must move at the slower person's pace. The question is, how can they all get across the bridge safely at night if the torch lasts only 15 minutes?

For example,

Person A and Person C could cross together (this would take 5 minutes)

Person A could bring the torch back alone (this would take 1 minute)

Person B and Person D could cross together (this would take 8 minutes)

Person B could bring the torch back alone (this would take 2 minutes)

Person A and Person B could cross together (this would take 2 minutes)

In theory they’re all across the bridge now but it took longer than 15 minutes so the torch would have burned out before they were all across. So this is not a correct solution.

Can you find a way for everyone to cross without the torch burning out?