Foundations of Arithmetic: Chapter Test
20 multiple-choice questions and 10 core practice problems, drawn from across the chapter and mixed together.
Multiple choice
20 questions, 100 points in total, 5 points each. Answer in any order and change your mind as often as you like. When you submit, your answers lock and every question shows its worked solution.
Core practice
10 problems from across the chapter. Work on paper, use hints when you need them, and check the answer or the full solution when you are ready.
Difficulty: Core (core-course level)
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Problem 1 Changed counter digit
A counter displays . Its is replaced by , with every other digit left in the same position. How much does the displayed number decrease?
- Hint 1
A digit contributes an amount determined by its position.
- Hint 2
Locate the by counting places from the right, then multiply by that place value.
Answer
.
Full solution
The is in the thousands place.
Its contribution is
Replacing that digit with removes its contribution and preserves the other places.
The new display is .
Check by restoring the removed amount:
Answer
.
Key idea
Replacing one digit by zero removes that digit's value when all other digits keep their positions.
- Hint 1
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Problem 2 Power and quotient
Evaluate .
- Hint 1
Identify the highest operation tier before starting.
- Hint 2
Evaluate the power, then work through division and multiplication from left to right.
Answer
.
Full solution
The exponent counts two factors of .
Division and multiplication share a tier, so divide before multiplying here.
As a check, four groups of make , and two copies of that quotient make .
Answer
.
Key idea
Evaluate powers before multiplication and division, then work left to right within their shared tier.
- Hint 1
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Problem 3 Ribbon for a club
Ribbon is sold in 30-meter rolls. A club orders 9 rolls, and the supplier cuts 2 meters from every roll before delivery. How many meters of ribbon does the club receive?
- Hint 1
Every roll loses the same length before delivery.
- Hint 2
Find what 9 full rolls would hold, then remove the 2 meters cut from each of the 9 rolls.
Answer
252 meters.
Full solution
Each delivered roll holds meters, so the club receives meters.
The cut comes off every roll, so the factor multiplies the as well as the .
Check by finding one delivered roll first: , and
Answer
252 meters.
Key idea
A cut taken from every roll is multiplied by the number of rolls, just as the full length is.
- Hint 1
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Problem 4 Swapped counter places
A machine stores a count equal to . A fault swaps its hundreds and tens digits while leaving all other digits in place. Write the faulty count in expanded form and determine whether it is smaller or larger than the original.
- Hint 1
An absent contribution still needs a digit in the numeral.
- Hint 2
Write the original numeral with its zero digit, then exchange the hundreds and tens digits.
- Hint 3
Compare the two numerals from the left until their digits differ.
Answer
; smaller, with .
Full solution
The original has 5 thousands, 6 hundreds, no tens and 9 ones, so it is .
The swap puts in the hundreds place and in the tens place.
The thousands digits agree.
The hundreds digits are the first to differ: the faulty count has where the original has .
Therefore
The fault changes the contribution of the from to .
That decrease agrees with the comparison.
Answer
; smaller, with .
Key idea
Swapping a digit with a zero changes its contribution, and the first differing place settles the comparison.
- Hint 1
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Problem 5 A four-step number machine
A number machine starts with . It adds , multiplies the result by , multiplies that result by , and finally adds . Find its output, and decide whether a different whole-number starting value would change it.
- Hint 1
Consider what each operation does to the current value, especially when the multiplier changes.
- Hint 2
Adding and multiplying by preserve the current value. Follow the operation that comes next.
Answer
; every whole-number starting value gives the same output.
Full solution
Adding zero and multiplying by one leave the starting value unchanged.
Multiplying by zero then removes its effect.
For any whole-number input, the first two steps preserve it and the third step produces .
The last step therefore produces for every such input.
Check with a different starting value, : all three initial steps leave , followed by the same final addition.
Answer
; every whole-number starting value gives the same output.
Key idea
Multiplication by zero makes the final value independent of the starting input when the later operations are fixed.
- Hint 1
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Problem 6 A stacked expression
Evaluate .
- Hint 1
The fraction bar groups the entire numerator and the entire denominator.
- Hint 2
In the numerator, settle the parentheses before the power and the outside multiplication.
- Hint 3
After evaluating the denominator, divide the completed numerator by it.
Answer
.
Full solution
Start with the innermost group, then evaluate its square and the multiplication.
The denominator is a separate group.
The denominator is , which is nonzero, so divide the completed numerator by it.
Check that the quotient times the denominator recovers the numerator:
Answer
.
Key idea
A fraction bar keeps its numerator and denominator grouped while the operation tiers govern each group.
- Hint 1
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Problem 7 Updating identical packets
A volunteer has 18 pencils and 30 erasers. She makes the greatest possible number of identical packets, using every item. Each packet must contain the same positive number of pencils and the same positive number of erasers.
She then puts 2 additional erasers into every packet. How many packets are there, and how many items are in all the updated packets combined?
- Hint 1
The packet count must divide both original item counts exactly.
- Hint 2
Find the greatest possible packet count first, then find the contents of one packet.
- Hint 3
Update the eraser count in one packet before counting each item type across all packets.
Answer
6 packets; 60 items.
Full solution
The packet count divides both and .
The divisors of are , , , , and .
Of these, and do not divide , but does.
Thus the greatest possible count is 6 packets.
Find the original contents of each packet.
The original total can be written as
Each updated packet has 3 pencils and erasers.
Count both parts across all 6 packets.
Check the change against the original total.
There were items and 2 erasers were added to each of 6 packets.
Answer
6 packets; 60 items.
Key idea
The greatest shared divisor determines the packet count, and updating each packet changes the totals for every copy.
- Hint 1
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Problem 8 A proposed rewrite
A student replaces with . Find the value of each expression and decide whether the replacement preserves the value. Explain your decision.
- Hint 1
Check which quantities are multiplied by the outside in each expression.
- Hint 2
In the first expression, evaluate the inner division and then the entire bracket.
- Hint 3
In the second expression, complete its multiplication and division before its addition.
Answer
and , respectively; the replacement does not preserve the value.
Full solution
The bracket groups both and the quotient for multiplication by .
In the replacement, the multiplies just the .
The replacement leaves the quotient unmultiplied by .
To preserve the first expression, both parts must receive that factor.
The two values, and , disagree, so the replacement does not preserve the value.
Answer
and , respectively; the replacement does not preserve the value.
Key idea
Dropping the brackets around a group that a factor multiplies requires that factor to multiply every term of the group.
- Hint 1
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Problem 9 Testing a general claim
A learner notices that swapping the inputs in leaves its value unchanged. The learner also notices that and have the same value.
The learner concludes that subtraction is commutative and division is associative. For each conclusion, say what was special about the learner's example, and give a counterexample to each conclusion that fails. For the division counterexample, use positive whole numbers with exact whole-number quotients in both groupings.
- Hint 1
A property must hold for every allowed choice of numbers, so a successful example does not establish it.
- Hint 2
To test the subtraction claim, try reversing two unequal whole numbers.
- Hint 3
To test the division claim, choose a divisor greater than inside the group and compare the two groupings.
Answer
The subtraction example used two equal numbers, and the division example divided by . Neither conclusion is valid; for example, and .
Full solution
The subtraction example uses equal inputs, so swapping them does not change the written calculation.
Unequal inputs reveal the failure.
But takes more than the available and goes below zero, so it is not .
This is a counterexample to commutativity.
The division example uses , which leaves the values unchanged in both groupings.
Instead compare these exact divisions.
Group the first pair:
Group the last pair:
Every divisor in the example is positive and nonzero, and every quotient is a whole number.
The two groupings give and , so division fails associativity.
One failing example is enough to reject each general conclusion.
Answer
The subtraction example used two equal numbers, and the division example divided by . Neither conclusion is valid; for example, and .
Key idea
A successful example can illustrate a property, but a single counterexample disproves a claim that it holds in every case.
- Hint 1
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Problem 10 Ravi's two lines
Ravi writes . He then replaces with , saying that the inside can still be divided by .
Decide whether each line preserves the original sum and whether the first line has the greatest common factor of and outside the parentheses. Explain your decisions.
- Hint 1
An outside factor must reproduce both original terms, not just the first one.
- Hint 2
Check what each outside factor gives when multiplied by each inside number.
- Hint 3
A further whole-number factor must divide both and .
Answer
The first line preserves the sum and has the greatest common factor, , outside; the replacement does not preserve the sum.
Full solution
The first line reproduces both original terms.
The possible divisors of greater than are and , and neither divides .
Thus and share no factor greater than , so is already the greatest shared factor removed from the original terms.
The replacement still reproduces but changes the other term.
Doubling the outside factor would require halving both inside terms to preserve their contributions.
Ravi halves just one, so his replacement changes the sum.
Check the valid expression directly:
Answer
The first line preserves the sum and has the greatest common factor, , outside; the replacement does not preserve the sum.
Key idea
A common factor is fully collected when the remaining whole-number terms share no factor greater than one.
- Hint 1