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Problem 146

Number theory Difficulty 1.4 Multiple choice CEMC Pascal · Canada · 2016

An oblong number is the number of dots in a rectangular grid with one more row than column. The first four oblong numbers are 2, 6, 12, and 20, and are represented below:

What is the 7th oblong number?

Pick one

Official solutions — 2

Solution 1

The 7th oblong number is the number of dots in retangular grid of dots with 7 columns and 8 rows.

Thus, the 7th oblong number is $7 \times 8 = 56$ .

Solution 2

The 7th oblong number is the number of dots in retangular grid of dots with 7 columns and 8 rows.

Thus, the 7th oblong number is $7 \times 8 = 56$ .

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.