9. word problem: a box has 4 rows of 6 markers each. each marker costs $1.25. write an expression to…

Explanation:

Step1: Find total number of markers

First, find the total number of markers. There are 4 rows with 6 markers each, so total markers = (4\times6).

Step2: Write expression for total cost

Each marker costs ($1.25), so total cost expression is ((4\times6)\times1.25) or (4\times6\times1.25). We can also use the associative property (or distributive property in another way) to compute mentally. Let's rewrite it using distributive property: (4\times6\times1.25 = 4\times1.25\times6) (commutative property of multiplication) (=(4\times1.25)\times6).

Step3: Evaluate using distributive/associative

Calculate (4\times1.25 = 5), then (5\times6 = 30). Alternatively, using distributive property on (6\times1.25=(5 + 1)\times1.25=5\times1.25+1\times1.25 = 6.25+1.25 = 7.5), then (4\times7.5 = 30).

Answer:

Expression: (4\times6\times1.25) (or equivalent like ((4\times6)\times1.25))
Total cost: ($30)

For mental computation with distributive property: We can break down (6\times1.25) as ((5 + 1)\times1.25=5\times1.25+1\times1.25 = 6.25 + 1.25 = 7.5), then multiply by 4: (4\times7.5 = 30). Or break down (4\times1.25 = 5) (since (4\times1 + 4\times0.25=4 + 1 = 5)) and then (5\times6 = 30).