1 marble costs $9.
For every 10 marbles bought, a discount of $5 is given.
- How much do 10 marbles cost?
- How much do 17 marbles cost?
- How much do 39 marbles cost?
(a)
Cost of every 10 marbles
= 10 x 9 - 5
= 90 - 5
= $85
(b)
Number of marbles that do not belong to a set
= 17 ÷ 10
= 1 r 7
Cost of the 7 extra marbles
= 7 x 9
= $63
Cost of 17 marbles
= 85 + 63
= $148
(c)
Number of sets of 10 marbles
= 39 ÷ 10
= 3 r 9
Cost of 30 marbles
= 3 x 85
= $255
Cost of 9 marbles
= 9 x 9
= $81
Cost of 39 marbles
= 255 + 81
= $336
Answer(s): (a) $85; (b) $148; (c) $336