How many 3 inch bottles did James buy?

Question

James bought 16 bolts at the hardware store for total of $6. Some were 3 inch bolts that cost $0.36 each and the others were 4 inch boats that cost $0.42 each. How many 3 inch bolts did James Buy

Answer 1

x = 3 inch bolts

 

y = 4 inch bolts

 

x + y = 16

 

y = 16 - x      1st equation

 

.36x + .42y = 6.00   2nd equation

 

substitute 1st equation into 2nd equation

 

.36x + .42(16 - x) = 6.00

 

.36x + 6.72 - .42x = 6.00

 

6.72 - .06x = 6.00

 

subtract 6.72 from each side

 

-.06x = -.72

 

x = 12

 

He bought 12 3-inch bolts

 

(so he bought 4 4-inch bolts)