1 marble costs $8.
For every 10 marbles bought, a discount of $7 is given.
- How much do 10 marbles cost?
- How much do 18 marbles cost?
- How much do 39 marbles cost?
(a)
Cost of every 10 marbles
= 10 x 8 - 7
= 80 - 7
= $73
(b)
Number of marbles that do not belong to a set
= 18 ÷ 10
= 1 r 8
Cost of the 8 extra marbles
= 8 x 8
= $64
Cost of 18 marbles
= 73 + 64
= $137
(c)
Number of sets of 10 marbles
= 39 ÷ 10
= 3 r 9
Cost of 30 marbles
= 3 x 73
= $219
Cost of 9 marbles
= 9 x 8
= $72
Cost of 39 marbles
= 219 + 72
= $291
Answer(s): (a) $73; (b) $137; (c) $291