Problem
Ten of a unit carries to the next place
Add up the money in a piggy bank that holds 12 hundred-dollar bills, 33 ten-dollar bills, 45 one-dollar coins, and 39 dimes, then give the grand total.
Base-ten numbers
Your answer
dollars
Watch out It's tempting to just add the four counts (12+33+45+39) instead of multiplying each one by its own bill or coin value first.
How to solve
Strategy Identify Subproblems — Find the value of each bundle separately (count times unit value), watching the units carefully because dimes are tenths of a dollar, then add the four amounts.
1STEP 1
Value of the hundred-dollar bills
12 bills of 100 each are worth 12 × 100 = 1,200.
12 × 100 = 1,200
Each bill is one hundred, so twelve of them is twelve hundreds.
4.NBT.A.1Analyze The Units2STEP 2
Value of the ten-dollar bills
33 bills of 10 each are worth 33 × 10 = 330.
33 × 10 = 330
Ten dollars repeated 33 times shifts 33 up one place to 330.
4.NBT.A.1Analyze The Units3STEP 3
Value of the one-dollar coins
45 coins of 1 each are worth 45 × 1 = 45.
45 × 1 = 45
Forty-five ones is just $45.
4.NBT.A.1Analyze The Units4STEP 4
Value of the dimes
39 dimes of 0.10 each are worth 39 × 0.10 = 3.90.
39 × 0.10 = 3.90
Ten dimes bundle into one dollar, so 39 dimes regroup into $3.90.
4.NBT.A.1Analyze The UnitsThe 39 dimes in the piggy bank are worth $3.90.
Why?
The worth of the 39 dimes is one dime's value counted 39 times over.
🧱Multiplication as equal groupsa times b means a equal groups of b — it is just repeated adding of the same amount.
Why?
One dime is one tenth of a dollar, so 39 dimes make 39 tenths of a dollar.
Why?
Ten equal dimes stack up to exactly one dollar, so each dime is one of ten equal parts of a dollar.
🧱Place-value groupingTen ones make one ten and ten tens make one hundred — each place bundles ten of the last.
Why?
39 tenths of a dollar is 3 whole dollars with 9 tenths left over, which we write as $3.90.
Why?
Every ten tenths bundle together into one whole dollar, so thirty of the tenths become 3 dollars and 9 tenths stay behind.
🧱Place-value groupingTen ones make one ten and ten tens make one hundred — each place bundles ten of the last.
5STEP 5
Add the four amounts
Total = 1,200 + 330 + 45 + 3.90 = 1,578.90 dollars.
1,200 + 330 + 45 + 3.90 = 1,578.90
Summing the separate bundle values gives the whole piggy bank.
4.NBT.A.2Identify SubproblemsAnswer
1,578.90 dollars
1,200 + 330 + 45 + 3.90 = 1,578.90
The big bundles dominate: 1,200 plus 330 is already 1,530, plus 45 and a few dollars of dimes lands near 1,579, which matches 1,578.90. Units stay in dollars throughout.
Takeaway
This only needs Grade 4 place-value sense: each bundle is its count times its value, and ten of one unit climbs to the next!
- Value of the hundred-dollar bills
- Value of the ten-dollar bills
- Value of the one-dollar coins
- Value of the dimes
- Add the four amounts
Where next?
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