NBT5-21 Word Problems I - JUMP Math

NBT5-21 Word Problems I

Page 53

STANDARDS 5.NBT.B.5

Goals

Students will solve word problems involving multiplication that may require multiplying multi-digit numbers by 1-digit numbers.

PRIOR KNOWLEDGE REQUIRED Can use the standard algorithm to multiply multi-digit numbers by

1-digit numbers

(MP.2, MP.4) (MP.2, MP.4)

Extensions

NOTE: In the extensions below, encourage students to model the situation using equations (MP.4) and to state what their equations mean in the context of the problem (MP.2).

1. Tim earns $9 per hour at his summer job.

a) How much does Tim earn in a 40-hour week?

b) How much will he earn in 8 weeks?

c)How many more weeks will he need to work to buy computer equipment that costs $3,600?

Selected sample solution: c) Since Tim has already earned $2,880, we can subtract to find the amount of money he still needs. 3,600 - 2,880 = $720. Tim needs to work 80 more hours (9 ? 80 = 720). Since he works 40 hours each week, he needs to work for 2 more weeks (40 ? 2 = 80).

Answers: a) $360, b) $2,880

2.A T-shirt company sold 1,250 T-shirts for $8 each. For each T-shirt, the company's costs were $2. What profit did the company make on the T-shirts? (Profit is the money the company earns minus its costs.)

Sample solutions ? The company's earnings can be found by multiplying the number

of T-shirts sold by the price of each T-shirt. 1,250 ? 8 = $10,000. Since the company's costs for each T-shirt was $2 and they sold 1,250 T-shirts, their total costs can be found by multiplying 1,250 ? 2 = $2,500. Subtract the total costs from the total earnings to get the company's profit: 10,000 - 2,500 = $7,500. ? Since the company sold each T-shirt for $8 but their costs were $2 per T-shirt, their profit will be $6 per T-shirt (8 - 2 = 6). So for 1,250 T-shirts, their profit is 1,250 ? 6 = $7,500.

Whole-class follow-up: Present the solutions above in order or have volunteers do so. ASK: Which solution is faster? (the second one) Which solution might be easier to think of? (the first one)

Number and Operations in Base Ten 5-21D-35

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