Mrs Lim bought a number of plates at an average price of $6. She decided to buy another plate which cost $18. The average price of all the plates then became $8. What was the total number of plates Mrs Lim bought in all?

 6

Step-by-step explanation:

Let x represent the number of plates bought for $6

Let y represent the Total number of plates bought = x + 1

Remember that Mrs. Lim bought another plate for $18

Total cost ÷ Total plates = Average Cost

6x + 18 = 8(x + 1)

6x + 18 = 8x + 8

       18 = 2x + 8

       10 = 2x

        5 = x

y = x + 1

  = 5 + 1

  = 6

use this formula:

p(a\b) = p(a and b)/p(b).

take it from here.