The first number is 1 and the last is: \(51\cdot2+1=101\)

So their sum is \(\dfrac{\left(101+1\right)\cdot51}{2}=2601\)

The first number is 1 and the last is: 51⋅2+1=101

So their sum is (101+1)⋅512=2601

List the number have exactly 1 number 8 from 100 to 400 : 108, 118, 128, 138, 148, 158, 168, 178, 180, 181, 182, 183, 184, 185, 186, 187, 189, 198, 208, 218, 228, 238, 248, 258, 268, 278, 280, 281, 282, 283, 284, 285, 286, 287, 289, 298, 308, 318, 328, 338, 348, 358, 368, 378, 380, 381, 382, 383, 384, 385, 386, 387, 389, 398 ( 188, 288, 388 is elminate because have 2 8s)

So there are 54 number have exactly 1 number 8 from 100 to 400

The positive integer divisors of 20 are 1,2,4,5,10,20
The positive integer divisors of 30 are 1,2,3,5,6,10,15,30
So the chances are \(4\cdot\dfrac{1}{6}\cdot\dfrac{1}{8}=\dfrac{1}{12}\)

Put : Almors = a

We have:

Brons = a + 20%a = 120%a

Choops = 120%a - 60% = 60%a

<=>\(\dfrac{a}{60\%a}=\dfrac{1}{60\%}=166,\left(6\right)\%\)

The answer is : \(166,\left(6\right)\%\)

We give : Almors is 100

=> Brons  = 100 . (100 . 20%) = 120

=> Choops = 120 . 50% = 60

Percentage of Almors and Choops are:

( 100 . 100 : 60 ) : 100 = 15,(5)%

The answer is : 15,(5)%

We have : abcabc = abc x 1001 = abc x 7 x 11 x 13

Because abc is a prime number,the number of divisors of abcabc is :

(1 + 1)4 = 16

Because abc is a prime number,the number of divisors of abcabc is :

(1 + 1)4 = 16

We have : abcabc = abc x 1001 = abc x 7 x 11 x 13

Because abc is a prime number,the number of divisors of abcabc is :

(1 + 1)4 = 16

When starting, the motorist goes in :

           60 : 20 = 3 ( hours)

When to return, the motorist goes in :

          60 : 30 = 2 ( hours )

In the entire trip, the motorist goes in :

           3 + 2 = 5 ( hours )

Medium speed of the motorist for the entire trip :

           60 : 5 = 12 (  miles per hour )

                          Answer : 12 miles per hour

me 12 too

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When starting, the motorist goes in :

                      60 : 20 = 3 ( hours)

When to return, the motorist goes in :

                         60 : 30 = 2 ( hours )

In the entire trip, the motorist goes in :

                       3 + 2 = 5 ( hours )

Medium speed of the motorist for the entire trip :

                 60 : 5 = 12 (  miles per hour )

                                         Answer : 12 miles per hour

\(\dfrac{3}{15}=\dfrac{a}{20}=\dfrac{24}{b}\)\(\Rightarrow\left\{{}\begin{matrix}3b=24.15\\15a=3.20\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}b=120\\a=4\end{matrix}\right.\)

\(\Rightarrow a+b=4+120=124\)

really

The total heights of 16 girls is : \(63,7\cdot16=1019,2\left(inches\right)\)

The total heights of 16 boys is  : \(65,4\cdot14=915,6\left(inches\right)\)

The mean of the heights of all 30 students is : \(\dfrac{1019,2+915,6}{30}\approx64,5\left(inches\right)\)

The answer is : 83 x 751 = 62333