Xiaoying is going to use 21 yuan to buy pens and notebooks. It is known that each pen costs 3 yuan and each notebook costs 2.2 yuan. She has bought two notebooks. Please help her to calculate. How many pens can she buy?

Xiaoying is going to use 21 yuan to buy pens and notebooks. It is known that each pen costs 3 yuan and each notebook costs 2.2 yuan. She has bought two notebooks. Please help her to calculate. How many pens can she buy?

Suppose she can also buy x pens, from the meaning of the question, 3x + 2 × 2.2 ≤ 21, the solution is: X ≤ 5815

So and so bought 5 rubbers and 3 pens, a total of 21 yuan, 4.5 yuan per pen, how many yuan per rubber?

（21-4.5×3）÷5
=（21-13.5）÷5
=7.5÷5
=1.5 yuan
A: 1.5 yuan per rubber

Xiao Ming pays 5.8 yuan for 4 pens and 7 exercise books. If one pen is replaced by one exercise book, he still needs to pay 0.2 yuan. What's the unit price of the exercise book?

Another 0.2 yuan = an exercise book costs 0.2 yuan more than a pen
Set a pen X Yuan, an exercise book (x + 0.2) yuan
4x+7(x+0.2)=5.8
4x+7x+1.4=5.8
11x=5.8-1.4
11x=4.4
x=0.4
0.4 + 0.2 = 0.6 yuan, unit price 0.6 yuan

How do four 7S make up 24
Four 7 with add subtract multiply divide bracket combination is equal to 24, each 7 can only be used once!
Seems to be using a more ingenious method!
Don't say it's possible, just say what you know!

No way

The operation of 3, - 5, - 11,7 is equal to 24

（-11）*（-5）-7*3=24

2. 3, 7 and 9 are equal to 24

(7－2)×3＋9＝24

How many minutes is 7 / 24 hours?

17.5 minutes

How can 5 5 8 9 be equal to 24

5*5+8-9

How can 3, - 5,8 and - 13 be equal to 24

-13-8*(-5)-3=24

How is 9.9.8.7 equal to 24

This combination can not be calculated, belongs to the poker 24 points in the no solution combination
When you can't figure it out, you can ask the computer for help