Question

1
2 3
4 5 6
7 8 9 10
................
....................
1. Write the next two lines of the pattern above.
2. Write the first and the last numbers of the 10th line.with explaination
3. Find the sum of all the numbers in the first ten lines.

Answer 1

Answer:

1. 11, 12, 13, 14, 15 and 16, 17, 18, 19, 20, 21

2. 1st no. Of 10th line 46, last no. Of 10th line 55

3. Sum upto 55 = 1540

Step-by-step explanation:

2. Last no. any line "n"

$\frac{n(n + 1)}{2}$

So last no. Of 9th line =

$\frac{9 \times 10}{2}$

= 45

So 1st no. Of 10th line = 45+1=46

Last no. Of 10th line =

$\frac{10 \times11 }{2}$

=55

3. Sum upto "n" th number=

$\frac{n \times (n + 1)}{2}$

Sum upto 55 =

$\frac{55 \times 56}{2}$

= 1540

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