Buy 3 pens in a stationery shop and get 2 free pens, 4 yuan each. How much should I pay for 12 pens?

Buy 3 pens in a stationery shop and get 2 free pens, 4 yuan each. How much should I pay for 12 pens?

Buy three and get two free,
So buy six and get four free, and buy two more
It only costs 6 + 2 = 8 pens
therefore
It's a minimum to buy 12 of these pens
4*8
=32 yuan

Using the law of multiplicative distribution to calculate: 20 × 55 = 24 × 205

20×55
=20×(50+5)
=20×50+20×5
=1000+100
=1100
24×205
=24×(200+5)
=24×200+24×5
=4800+120
=4920

Given 6sin & sup2; α + 5sin α cos α - 4cos & sup2; α = 0, α ∈ (3 π / 2,2 π), find the value of Tan α

6sin²α+5sinαcosα-4cos²α=0
（2sina-cosa)(3sina+4cosa)=0
2sina cosa = 0 or 3sina + 4cosa = 0
2sina=cosa
tana=1/2
Or 3sina = - 4cosa
tana=-4/3
Because α ∈ (3 π / 2,2 π),
So Tana

The grassland is 18 meters long and 10 meters wide, with two even paths 2 meters wide in the middle

18×10）－（18×2＋10×2－2×2）
=180－52
=128 (M2)
A: the actual area of grassland is 128 square meters

What's the ratio of one in five to five in seven

1/5÷5/7
=1/5×7/5
=7/25.

Two sequences {an} and {BN} satisfy BN = a1 + 2A2 +... + Nan / 1 + 2 +... + n,
If {an} is an arithmetic sequence, then the sequence {BN} is also an arithmetic sequence, which requires that the formula can not be obtained by adding the square of 1 to the square of 2

It seems that we can't avoid this formula

If a room is paved with 30cm long square bricks, 100 pieces are needed. If a room is paved with 50cm long square bricks, how many pieces are needed?

Let x block be required, 30 × 30 × 100 = 50 × 50 × x, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 2500x = 900 × 100, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 2500x = 90000, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 36; a: 36 blocks are required

"Fifty six nationalities, fifty-six flowers, fifty-six brothers and sisters are a great urgency
Up and down five thousand years, the great homeland of China. "Fifty six nationalities, fifty-six flowers, fifty-six brothers and sisters are one family."
A the Chinese nation is a nation with a long history. B the status of all ethnic groups in our country is equal
C our 56 nationalities have their own characteristics d our country is a unified multi-ethnic country
Why B

The key point of this sentence is in the last sentence [brothers and sisters of 56 nationalities are one family], which means that all nationalities have equal status, so choose B

Let the coordinates of a point P on the terminal edge of angle α be (COS π / 5, sin π / 5), then α=
Let the coordinates of a point P on the terminal edge of angle α be (- cos π / 5, - sin π / 5), then α=
Let the coordinates of a point P on the terminal edge of angle α be (sin π / 5, - cos π / 5), then α=

Let the coordinates of a point P on the terminal edge of angle α be (COS π / 5, sin π / 5), then α = π / 5

If the three median lines of the triangle are 2cm, 3cm and 4cm respectively, the perimeter of the original triangle is______ ．

∵ the perimeter of the triangle composed of three median lines is 2 + 3 + 4 = 9cm, and the perimeter of the original triangle is 2 × 9 = 18cm