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Every hour on the hour, Helen does jumping jacks. At 4:00 she does 4 jumping jacks. At 5:00 she does 5 jumping jacks, etc. How many jumping jacks will Helen do, in total, from the time prior to her final jumping jacks at 4:00 to the time prior to her first jumping jacks at 11:00 ?a) 46b) 56c) 57d) 60

Answer :

We have to add the jumping jacks from 4:00 (not included) to 11:00.

So we have to add:

[tex]\sum ^{11}_{n\mathop=5}n=5+6+7+8+9+10+11=56[/tex]

The answer is option b) 56.

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