1 marble costs $7.
For every 10 marbles bought, a discount of $4 is given.
- How much do 10 marbles cost?
- How much do 19 marbles cost?
- How much do 21 marbles cost?
(a)
Cost of every 10 marbles
= 10 x 7 - 4
= 70 - 4
= $66
(b)
Number of marbles that do not belong to a set
= 19 ÷ 10
= 1 r 9
Cost of the 9 extra marbles
= 9 x 7
= $63
Cost of 19 marbles
= 66 + 63
= $129
(c)
Number of sets of 10 marbles
= 21 ÷ 10
= 2 r 1
Cost of 20 marbles
= 2 x 66
= $132
Cost of 1 marbles
= 1 x 7
= $7
Cost of 21 marbles
= 132 + 7
= $139
Answer(s): (a) $66; (b) $129; (c) $139