Issac's backpack weighed 75.5 ounces. if he removes one ipod that weighs 4.9 ounces and the ipad which weighs 25.6 ounces, how much does issac's backpack now weigh?

First subtract the iPod weight 75.5-4.9=70.6,then subtract the IPad weight 70.6-25.6 and your final answer is 45

Okay so the fist thing you need to do is figure out how much the Ipod and Ipad weighs together. 
Do this by adding their weights:
4.9+25.6=30.5

Now you need to subtract that from how much the total weight of the backpack was:
75.5-30.5=45

So your answer would be 45 oz. 
Hope this Helps

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