One million to seven
Problem
Start by putting one million ($1 000 000$) into the display of your calculator.
Can you reduce this to $7$ using just these six buttons - the $7$ key and add, subtract, multiply, divide and equals as many times as you like?
What is the shortest way can you find to do it?
Getting Started
Try using numbers like $777$.
How will you keep track of what you have done?
Student Solutions
Many of you have had an excellent stab at this problem - it requires a lot of perseverance - and you have come up with several ways, all of which take four steps. Matthew from Gayhurst School suggests:
$1 000 000 \times 7 = 7 000 000$$7 000 000 + 777 777 = 7 777 777$
$7 777 777\div 7 777 777 = 1$
$1 \times 7 = 7$
Tom, who goes to The Oratory Preparatory School found a different way which is equally as quick:
$1000000\times77=77000000$$+777777=77777777$
$\div 77777777=1$
$\times7 =7$
Yet another way was discovered by Robert from U-Hill Secondary and pupils from the Sutton Masterclass:
$1 000 000 \times 7 = 7 000 000$$7 000 000 + 777 777 = 7 777 777$
$7 777 777 - 7 777 777 = 0$
$0 + 7 = 7$
Pupils from Moorfield Junior School told us about a fourth way:
$1,000,000\times 7 =7,000,000$$7,000,000 - 7,777,777 = -777,777$
$-777,777 + 777,777 = 0$
$0 + 7 =7$
Theo, Matthew, Seth and Jessie from Christ Church Primary School went about it in this way:
$1 000 000\div 77 777 777 = 0.0128571$This is interesting. I'm particularly intrigued by the second line. I wonder why the calculator display gives zero?
Fantastic - and to think it looked so difficult!
Teachers' Resources
Why do this problem?
Possible approach
Key questions
Possible extension
After they have found at least four ways of doing this, learners could try Two and two or even the Stage 3 problem Arrange the digits.
Possible support
Suggest using a simple calculator and experimenting quietly to see what happens or doing this two digit activity.