HW#1- Numbers & Arithmetic
(solutions)
Due: Wednesday March 30, 2011
HW #1- Solutions
Topics: numbers, addition, subtraction, multiplication, division, rounding, and
estimation
I. Numbers
1. Explain why we use the base 10 system and how it works using your own words.
[4 points]
We use the base 10 system since it is easy for us to learn, probably because we have
10 fingers on our hands. By placing a specific digit in a given place relative to the
decimal point we are able to represent different quantities of powers of 10. Thus the
number 342 represents 3 100’s, 4 10’s and 2 1’s.
2. Consider the number 385,290.20:
a. How many thousands (1,000’s) are in this number? [2 points]
There are 5 thousands in this number. Also acceptable was 385 thousands.
b. How many tenths
are in this number? [2 points]
There are 2 tenths in this number.
c. How many hundredths
are in this number? [2 points]
There are 20 hundredths in this number. Also acceptable was 0 hundredths.
II. Addition and Subtraction
3. Suppose for lunch Annie buys a grilled ham and cheese sandwich (22 baht), bottle of
water (7 baht), and bag of Kit-Kat bites (29 baht) at 7-11.
a. Without using a calculator, what is the total amount of money Annie must pay?
[5 points]
Annie must pay 22 + 7 + 29 baht which is the same as 29 + 29 baht which is
40 + 9 + 9 baht, which is 40 + 18 baht, which is 58 baht total.
b. Using the subtraction by making change method, which coins and bills will Annie
receive if she pays using a 500 baht bill? [5 points]
Annie will receive in change a 2 baht coin (58 + 2 = 60), two 20 baht bills
(60 + 40 = 100) and four 100 baht bills (100 + 400 = 500).
III. Multiplication and Division
4. Suppose Sue invites her friends over to her apartment for a pizza party. Since 5 of her
friends are coming over, she orders 3 large cheese pizzas from Pizza Company, as well as
2 orders of bread sticks with dipping sauce.
a. Using a calculator, if each pizza costs 475 Baht and each order of breadsticks costs
49 Baht how much does Sue owe Pizza Company? [5 points]
Sue owes 3 x 475Baht for the pizzas and 2 x 49Baht for the breadsticks for a
total of 1048Baht.
b. Each pizza has 8 slices. How many slices will each person get to eat (including Sue
there are 6 people)? [5 points]
There are 8 x 3 total slices, which is 24. Thus each person will get 24/6
slices, or 4 slices per person.
IGE104: Logic and Math for Daily Living (3-2010)
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HW#1- Numbers & Arithmetic
(solutions)
Due: Wednesday March 30, 2011
c. Each breadsticks order has 12 pieces. How many pieces will each person get to eat
(including Sue there are 6 people)? [5 points]
There are 12 x 2 total pieces, which is 24. Thus each person will get 24/6
pieces, or 4 pieces per person.
IV. Rounding
5. Elissa recently received a job offer from SweatShoppe Inc. with a starting salary of
11,298Baht per month. After trying to negotiate a higher salary, her boss agrees to round
her salary to the nearest 1,000.
a. What is the amount of Baht per month that her boss offering? [3 points]
Elissa’s Boss is offering a salary of 11,000Baht per month.
b. Should Elissa accept the offer of a rounded salary? [2 points]
Elissa’s should not accept his offer since the rounded salary is less than the
original salary he offered her.
6. Becky figures that she’ll need about 550 pounds of concrete for her new patio. To get the
best price on the concrete, she needs to buy it in one-hundred pound sacks. How many
hundred pound sacks should she buy? [5 points]
Becky should buy 6 sacks since this way she will have enough concrete for her new
patio.
V. Percents
7. Chelsea needs to buy a new motorcycle helmet. The original price of the helmet is
2,300Baht, but it is on sale for 20% off. Without using a calculator, how much does the
helmet cost? [5 points]
10% of 2,300 is 230baht. So 20% of 2,300 is just 460 baht. Thus if Chelsea pays 20%,
she will pay 2300 – 460 baht total, which is just 1,840 baht.
VI. Estimation
8. Emily wants to buy a used car with a price of 395,620 baht. The seller has agreed to let
her pay for the car in 12 monthly payments over the course of one year. Approximately
how much will she pay per month? [5 points]
395,620Baht is approximately 400,00 baht, and 12 months can be viewed as 10
months. So Emily will pay about 400,000/10 baht per month which will be ~
40,000baht/month.
BONUS
What is your email address? (Please write legibly) [2 points]
IGE104: Logic and Math for Daily Living (3-2010)
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