1 marble costs $3.
For every 10 marbles bought, a discount of $3 is given.
- How much do 10 marbles cost?
- How much do 18 marbles cost?
- How much do 31 marbles cost?
(a)
Cost of every 10 marbles
= 10 x 3 - 3
= 30 - 3
= $27
(b)
Number of marbles that do not belong to a set
= 18 ÷ 10
= 1 r 8
Cost of the 8 extra marbles
= 8 x 3
= $24
Cost of 18 marbles
= 27 + 24
= $51
(c)
Number of sets of 10 marbles
= 31 ÷ 10
= 3 r 1
Cost of 30 marbles
= 3 x 27
= $81
Cost of 1 marbles
= 1 x 3
= $3
Cost of 31 marbles
= 81 + 3
= $84
Answer(s): (a) $27; (b) $51; (c) $84