1 marble costs $5.
For every 10 marbles bought, a discount of $5 is given.
- How much do 10 marbles cost?
- How much do 15 marbles cost?
- How much do 21 marbles cost?
(a)
Cost of every 10 marbles
= 10 x 5 - 5
= 50 - 5
= $45
(b)
Number of marbles that do not belong to a set
= 15 ÷ 10
= 1 r 5
Cost of the 5 extra marbles
= 5 x 5
= $25
Cost of 15 marbles
= 45 + 25
= $70
(c)
Number of sets of 10 marbles
= 21 ÷ 10
= 2 r 1
Cost of 20 marbles
= 2 x 45
= $90
Cost of 1 marbles
= 1 x 5
= $5
Cost of 21 marbles
= 90 + 5
= $95
Answer(s): (a) $45; (b) $70; (c) $95