What addition doubles fact can help you solve 4 +5?
2 answers:
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Let 
be the amount of time it takes to perform an arm routine and 
be the amount of time it takes to perform an abdominal routine. We see:
Subtracting the second equation from the first gives
. Substituting gives 
, so 
and 
.
Thus, an arm routine takes ten minutes and an abdominal routine takes thirty minutes.
Subtracting the second equation from the first gives
Thus, an arm routine takes ten minutes and an abdominal routine takes thirty minutes.
