The question as given (to my brother) was the following

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Every cream pastry contains 430calories. If I walk briskly I will loose 5calories/minute. After eating 's' cream pastries and then walking briskly for 't' minutes, the calories 'c' which I would have consumed are given by:

c = 430s – 6t

(c=calories s=number of cream pastries t=number of minutes)

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By nature I assumed that there was a problem in the equation and it should have been

c=430s - 5t

Since you multiply 430 by the number of cream pastries you have eaten

and then subtract by 5*t (as you will loose 5 calories * number of minutes)

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I consulted with my lecturer which however denied that there is a mistake in the problem. Does anyone know any possible reason ?

Thanks a lot for any help.