Seventh Grade · Math · week 4

Percent increase and decrease

Compute percent increase and percent decrease, and use a percent change to find a new amount.

Percent change compares how much something changed to what it started as: percent change = (change)/(original) x 100. If the amount went up, it is a percent INCREASE; if it went down, it is a percent DECREASE.

You can also work backwards: to find a new amount after a known percent change, multiply the original by (1 + the rate) for an increase, or by (1 - the rate) for a decrease. Both directions use the exact same idea, just aimed differently.

📋 For the teacher
Teach it (10–15 min):
  • Drill the one rule: percent change always divides by the ORIGINAL (starting) amount, never the new amount.
  • Practice both directions in the same sitting: finding the percent change, and using a percent change to find a new amount.
  • Turn "increased by 20%" into a single multiplier (1.20) and "decreased by 15%" into (0.85) -- this shortcut saves a step every time.
  • Use real prices from a store flyer or app to make the numbers feel real instead of abstract.
Talk about it:
  • Why do you divide by the ORIGINAL amount and not the new amount?
  • How do you turn "increased by 30%" into one multiplier?
  • What is the difference between a 25% increase and a 25% decrease, starting from the same number?

Mastery looks like: They correctly compute a percent increase or decrease, and use a given percent change to find a new amount in either direction.

Common stumbles: Dividing by the new amount instead of the original; forgetting to add 1 (or subtract from 1) when computing the multiplier for a new amount.

Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
Records attendance + 15 min of Math for this learner.
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