Answer:
Number of postcards bought by Yoshi = 4
Explanation:
Number of stamps bought by Cindy = 20
Number of stamps bought by Cindy = Five times of the number of postcards bought by Yoshi.
Number of stamps bought by Cindy = 5 x Number of postcards bought by Yoshi.
5 x Number of postcards bought by Yoshi = 20
Number of postcards bought by Yoshi = 20/5 = 4
Number of postcards bought by Yoshi = 4
