AlgebraMediumBase of an isosceles triangle from its perimeter
Algebra practice question
An isosceles triangle has a perimeter of 46 centimetres. Each of its two equal sides is 5 centimetres longer than its base. What is the length of the base, in centimetres?
Answer: 12
Let the base be b; each equal side is b + 5: 2(b + 5) + b = 46 → 3b + 10 = 46 → b = 12.
Common wrong answers
- If you answered 17
- 17 is the length of each equal side.
- If you answered 15.33
- 15.33 is 46 ÷ 3, ignoring the 5-centimetre difference.
- If you answered 18.67
- 18.67 comes from 3b − 10 = 46, subtracting the 10 instead of adding it.
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