Rounding Decimals: Homework

Find the place, look one digit to the right, and watch for the times a number must go UP no matter what.

Part A — Plot and Round / 12

For 1 and 2, put a dot on the number line, then round. For 3 to 12, write the rounded number.

1.
Plot 6.38. Is it closer to 6.3 or 6.4? Round it to the nearest tenth.
Answer
2.
Plot 17.46. Which whole number is it closer to? Round it to the nearest whole number.
Answer
3.
5.27 to the nearest tenthAnswer
4.
18.643 to the nearest hundredthAnswer
5.
9.5 to the nearest whole numberAnswer
6.
0.0372 to the nearest thousandthAnswer
7.
82.449 to the nearest tenthAnswer
8.
4.996 to the nearest hundredthAnswer
9.
0.8051 to the nearest hundredthAnswer
10.
299.97 to the nearest tenthAnswer
11.
12.0449 to the nearest hundredthAnswer
12.
7.0961 to the nearest thousandthAnswer

Each of these has a trap. Look at only ONE digit, the one right next to the place.

1.
Round 6.449 to the nearest tenth. A student rounds 6.449 to 6.45, then 6.45 to 6.5. What is the real answer?Answer
2.
Round 3.96 to the nearest tenth. Does your answer still have a digit in the tenths place?Answer
3.
Round 1.296 to the nearest hundredth. Should the answer be written 1.3?Answer
4.
Round 5.6 to the nearest whole number. Ben says the 5 in the ones place stays, so it is 5. Is he right?Answer
5.
Round 8.5 and 8.49 to the nearest whole number. Do they land on the same number?Answer
6.
Which skill? Round 8.3333 to the nearest hundredth. Then a $22 bill is split among 3 friends: 22 ÷ 3 = 7.3333... Each friend must pay enough to cover the bill. What does each friend pay, and why is it not the nearest cent? (Rounding a decimal is U2-L2. Rounding a quotient is U2-L8.)Answer

These are real times from NASA's Planetary Fact Sheet: how many hours each planet takes to spin once.

Think it through, then write your answer and one sentence about how you knew.

1.
A school needs rides for 25 students, and each van seats 8. 25 ÷ 8 = 3.125. Rounding to the nearest whole number gives 3 vans. Does 3 vans work? What kind of rounding does this need, and name one other time in real life you would always round up.Answer
2.
A number rounds to 6.5 when you round to the nearest tenth. What is the smallest hundredths number it could be, and what is the greatest hundredths number it could be?Answer

Write your own, then solve it yourself.

1.
Write a decimal with three decimal places that rounds to a different number at the whole number, the tenth and the hundredth. Show all three roundings.Answer

Total / 27

Graded by

Notes

Part A — the rounded numbers.

Part B — the answer.

6.4. Only the 4 right next to the tenths place matters, so you never round twice.
4.0. The 9 goes up and carries, and the zero stays to show you rounded to tenths.
1.30. The zero on the end shows the number was rounded to hundredths.
No. Look at the digit to the right, 6, so the 5 goes up to 6.
No. 8.5 rounds up to 9, but 8.49 has a 4 next door, so it stays 8.
$7.34 each. The nearest cent is 7.33, but 3 × 7.33 = 21.99 is a cent short, so a bill rounds UP. (And 8.3333 to hundredths is 8.33.)

Part C — the answers.

a. 24.6 hours b. 9.93 hours c. 24 hours. Yes, that is the length of a day on the clock.
a. 3.142 b. 2.72 c. 1.6, and then 2

Part D — one correct answer, and what a good explanation says.

No. 3 vans seat only 24, so one student is left behind. You must round UP to 4 vans. Other times: buying boxes, tickets or paint, where a little left over is better than too little.
The smallest is 6.45 and the greatest is 6.54. 6.45 has a 5 next door so it rounds up to 6.5, and 6.55 would round up to 6.6.

Part E — what a good problem looks like.

Answers vary. A good one shows each rounding and they all differ, such as 3.648: whole number 4, tenth 3.6, hundredth 3.65.