MathGrade 5ages 10–11
✴️ Decimal times
A child who has only multiplied whole numbers may expect every multiplication to make the number bigger, so a decimal like 0.5 times 8 landing on 4 — smaller than 8 — feels wrong even when it is correct.
Try this lesson freeNo card needed. The first lesson is free.
Download on the App StoreWhat your child learns
- Multiplying by part of a whole gives a smaller result, not a bigger one.
- A half times eight is half of eight, which is four.
- To work it out, ignore the point, multiply like whole numbers, and put it back at the end.
- Count how many digits came after the points altogether, and the answer has exactly that many.
The mistake most kids make here
Assuming multiplying always makes things bigger, or forgetting to count places.
Try one question
How much is 0.5 times 8?
0.5 × 8
- 4
- 0.4
- 8.5
Answer
4 — Yes. Four.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: How do you know where to put the point in the answer?
How to help at home
This mix-up comes from a true rule that stops applying: whole-number multiplication always grows the number, but multiplying by part of a whole shrinks it. Half of eight is naturally four, not more than eight.
Cut a real object in half in front of your child — half a sandwich, half a chocolate bar — and ask how much that is compared to the whole one. Then connect it: "half times eight is asking for half of eight."
For the written method, have them multiply the digits as if there were no point at all (5 times 8 is 40), then count how many digits sat after the points in the question and move the point that many places in the answer.
A sign they have it: they can predict, before calculating, whether an answer will be bigger or smaller than the number they started with.
Questions parents ask
- Why does my child think 0.5 × 8 should be bigger than 8?
- They have generalized a true rule from whole-number multiplication — that multiplying always grows a number — to a case where it no longer applies. Multiplying by less than one shrinks the result.
- What is a simple way to practice multiplying decimals?
- Multiply as whole numbers first, ignoring the point, then count the total digits after the points in the question and place the point that many spots from the right in the answer.
- How can I check if a decimal multiplication answer is reasonable?
- Ask whether you are multiplying by more than one (answer grows) or less than one (answer shrinks), and compare the rough size before trusting the exact digits.
- How does Maya teach multiplying decimals?
- Maya starts from a real half-and-whole comparison so the child predicts smaller-not-bigger before ever touching the digit method.
No card needed. The first lesson is free.
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