Percent change

ATI TEAS
Math: Numbers and Algebra
Multiple choice
Difficulty 3 of 5

Question

A neighborhood walking club had 40 members in January and 58 members in July. By what percent did the club's membership increase?

18%✗ Incorrect

Incorrect. This answer gives the raw difference instead of a percent.
31%✗ Incorrect

Incorrect. This answer divides by the new value instead of the original value.
45%✓ Correct

Correct. Percent change = (new − old) ÷ old × 100 = (58 − 40) ÷ 40 × 100 = 45%.
145%✗ Incorrect

Incorrect. This answer gives the new value as a percent of the old value.

Answer

C. 45%

Rationale

Membership grew from 40 to 58, so the change is measured against the January total of 40. Divide the increase by 40 and multiply by 100. Writing the July total as a percent of the January total gives a number above 100, which describes relative size rather than the amount of change.

Worked solution: Percent change = (new − old) ÷ old × 100 = (58 − 40) ÷ 40 × 100 = 45%.

RememberNew ÷ old × 100 shows relative size; percent change is (new − old) ÷ old × 100.

Sources

DOE-HDBK-1014/1-92 U.S. Department of Energy · License: US government work (public domain) · Retrieved November 2, 2026 · Page 80
Guide for the National Institute of Standards and Technology · License: US government work (public domain) · Retrieved November 2, 2026 · Page 32
State Operations Manual Centers for Medicare & Medicaid Services · License: US government work (public domain) · Retrieved November 2, 2026 · Page 401
Lesson 3: Measures of Risk (Source: CDC) Centers for Disease Control and Prevention (CDC) · License: CDC content (credit required) · Retrieved November 2, 2026 · Vaccine efficacy or vaccine effectiveness; EXAMPLE: Calculating Vaccine Effectiveness

Last verified: November 5, 2026 2 independent automated checks Question teas-mna-00016, version 1

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