Urgent math help!!

Question

 

Some boys are sharing a packet of potato chips.if each boy eats 10 pieces there will be 3 pieces short.If each boy eats 9 pieces there will be 4 pieces left.How many pieces of potato chips are there in the packet?

Answer 1

Let P = # potato chips in the bag

Let B = # boys

 

If we try to give each boy 10 pieces we are 3 short so 10B = P+3 

If we give each boy 9 pieces, we then have 4 pieces left over so 9B = P-4

 

We have two simultaneous equations:

 

eqn 1)  10B = P+3

eqn2)     9B = P-4

 

Subtract eqn 1 from equation 1

 

  10B = P+3

  -(9B = P-4)

  --------------

     B = 7

 

There are 7 boys.

 

10B = P+3

10(7)=P+3

 70 = P+3

 P = 67

 

Check answer:  7 boys, 10 pieces each = 70 pieces which is 3 more than we have. 

                       7 boys, 9 pieces each = 63 pieces which is 4 less than we have.

                       That checks with the stated parameters.