Subtracting to 2008
Can you work out the sum of the missing digits in this subtraction?
Age
11 to 14
Challenge level
Problem
In this subtraction, $P$, $Q$, $R$ and $S$ are digits. What is the value of $P + Q + R + S\;$?
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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: P + Q + R + S = 16
Subtracting
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0 + 1 + 9 + 6 = 16
Adding
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so R+1 = 10 ie. R = 9, Q = 1 and P = 6, S = 0
9 + 1 + 6 + 0 = 16