money problem on pens

Question

At the rate, of 4 pens for C¢, how many pens can i buy for 40¢?

A) 10C
B)10/C
C)160/C
D) none of these

Answer 1

 

   4 pens costs C cents.

   4 pens = C cents

 

We can construct a proportion.  4 pens is to C cents, as 40 pens is to x cents

 

    4 pens        40  pens

   ----------- = --------------

    C cents        x cents

 

Note that the units (pens, cents) are in the same location (numerator, denominator on both sides of the proportion

Cross multiply and solve for x.

 

    4x = 40C

      x = 40C/4

      x = 10C

 

Thus, 40 pens would cost 10C cents

 

Answer 2

When you go to the store to buy one pen, it has a price.

When you buy 4 pens, the price is C cents.

 

Think! To buy 40 pens, you'd have to multiply the above fact (40 pens, C cents) by ten, to get 40 pens for ___ cents.