3 years ago

Why did Garrett Morgan invent the

1 answer:

5 0

Answer:

Smoke hood. Garrett Morgan invented a safety hood smoke protection device after seeing firefighters struggling from the smoke they encountered in the line of duty. ... Disguised as Big Chief Mason, he would enter the tent full of black smoke, and would remain there for 20 minutes before emerging unharmed.

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In a theater, there are 15 chairs in the first row, each row has 3 more chairs than the previous row, and there are 15 rows. how

Nimfa-mama [501]

The 1st row has 15 chairs.

The 2nd row has 15 + 3 = 18 chairs.

The 3rd row has 18 + 3 = 15 + 2•3 = 21 chairs.

The 4th row has 21 + 3 = 15 + 3•3 = 24 chairs.

The pattern continues, so that the n-th row has 15 + (n - 1)•3 = 3n + 12 chairs.

If there are 15 rows, then the total number of chairs is

$\displaystyle \sum_{n=1}^{15} (3n + 12) = 3 \sum_{n=1}^{15} n + 12 \sum_{n=1}^{15} 1 = 3\cdot\frac{15\cdot16}2 + 12\cdot15 = \boxed{540}$