Building up
In the diagram, the number in each box is obtained by adding the two immediately below. What is the number in the top box?
Age
11 to 14
Challenge level
Problem
In the diagram below, the number in each box is obtained by adding the numbers in the two boxes immediately underneath. What is the value of $x$?
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If you liked this problem, here is an NRICH task that challenges you to use similar mathematical ideas.
Student Solutions
Answer: 360
Putting in numbers
2 numbers which add up to 90
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2 other numbers:
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Guess that $x$ is always 360.
Method below is more complete (shows why):
Algebra
$a+b=90$
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