Rachel spent $70 more than Samuel. If Samuel spent $449, then how much did Rachel spend?
2 answers:
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Let g be the number of grandchildren, and d be the number of dogs. They both have only one head, so the number of heads is
Grandchildren have 2 legs, while dogs have 4. So, the total number of legs is
From the first equation (the one for the heads) we can derive
Substitute this into the second to get
So, there are 9 dogs and (from the first equation