1 marble costs $9.
For every 10 marbles bought, a discount of $3 is given.
- How much do 10 marbles cost?
- How much do 19 marbles cost?
- How much do 39 marbles cost?
(a)
Cost of every 10 marbles
= 10 x 9 - 3
= 90 - 3
= $87
(b)
Number of marbles that do not belong to a set
= 19 ÷ 10
= 1 r 9
Cost of the 9 extra marbles
= 9 x 9
= $81
Cost of 19 marbles
= 87 + 81
= $168
(c)
Number of sets of 10 marbles
= 39 ÷ 10
= 3 r 9
Cost of 30 marbles
= 3 x 87
= $261
Cost of 9 marbles
= 9 x 9
= $81
Cost of 39 marbles
= 261 + 81
= $342
Answer(s): (a) $87; (b) $168; (c) $342