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Class 8 Maths · Chapter 8 · NCERT (hegp201)

Fractions in Disguise: common misconceptions

See the tempting mistake students make in Fractions in Disguise, why it feels right at first glance, and a worked visual example that shows the right idea.

The tempting mistake & worked visual

Does a percent already give a count?

Wrong

A 25% discount always means 25 rupees off.

Why it feels right. I read 25% as a fixed amount.

Right

A percentage is a share of a specified whole.

Worked example

25% of ₹20050 rupees
25% of ₹400100 rupees
One quarter is the same fraction of both prices. The higher price has the bigger rupee discount.
  1. One quarter of ₹200 is ₹50.
  2. One quarter of ₹400 is ₹100.
  3. Both discounts are 25%.

If your child says… (8 concept checks in this chapter)

As you work through Fractions in Disguise, listen for these everyday misunderstandings and use the prompt alongside each one.

1. Per Cent, Per Decem and Per Mille See how to teach this step →

If your child says… “Five shaded columns means 5%.”

Ask together
When you count cells instead of columns, how many shaded parts are there?
What’s true
Count shaded parts and total parts using the same-sized pieces.

If your child says… “A percentage cannot go beyond 100%.”

Ask together
If this whole strip is 100%, what happens when the length extends beyond it?
What’s true
A length greater than the reference strip has a percentage greater than 100%.
3. Ratios and Percentages See how to teach this step →

If your child says… “Two heads and three tails means heads are two-thirds of the coins.”

Ask together
Are there three coins altogether, or five?
What’s true
The whole includes both heads and tails.
4. Proportions and Absolute Amounts See how to teach this step →

If your child says… “Both are 50%, so both pieces must be the same size.”

Ask together
Did the two starting portions contain the same amount of roti?
What’s true
Equal percentages can give unequal amounts when the wholes differ.
5. Successive Percentage Changes See how to teach this step →

If your child says… “A 50% rise and a 50% fall cancel.”

Ask together
Does the fall remove half of 4 rupees or half of 6 rupees?
What’s true
The fall takes half of a larger amount than the rise used.
6. Percentage Area See how to teach this step →

If your child says… “Three pieces always mean 75%.”

Ask together
What makes each piece here the same share of the sheet?
What’s true
Counting pieces gives area shares only when those pieces have equal areas.
7. Tax Added to a Bill See how to teach this step →

If your child says… “The tax calculation gives the whole bill.”

Ask together
Where does the original 20 rupees appear in the amount paid?
What’s true
The percentage calculation gives tax alone; the bill also includes the subtotal.
8. Peaceful Knights See how to teach this step →

If your child says… “Where can it land?”

Ask together
Which destination completes both the two-square part and the one-square part?
What’s true
The destination must complete both parts of the move.

Use this chapter three ways