Every published problem
All the published lessons, complete.
Free no sign-up
- No account and no personal data
- No limit on lessons
- New lessons are added to the list
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Pricing
Every published problem is free and needs no sign-up. You only pay to ask for the lesson of a new one.
Requests are not open yet and nothing is charged through the site. Write to me and I will let you know when they open.
A new problem · Pre-university (ages 16–18)
You ask for a problem that is not here and its lesson is prepared.
from €0.50 per problem, VAT included
| Standardwithin 3 calendar days | €0.50 |
|---|---|
| Priority 24 hwithin 24 hours | €1.00 |
| Priority 8 hwithin 8 hours | €1.50 |
A new problem · University
You ask for a problem that is not here and its lesson is prepared.
from €1.00 per problem, VAT included
| Standardwithin 3 calendar days | €1.00 |
|---|---|
| Priority 24 hwithin 24 hours | €2.00 |
| Priority 8 hwithin 8 hours | €3.00 |
The price is per problem, VAT included. Priority multiplies the base price: ×2 within 24 hours, ×3 within 8 hours.
Paid with prepaid credit
You are not charged problem by problem: you top up credit and each request is deducted from it according to the level and priority you choose.
Planned payment method for top-ups: PayPal. It is not active yet.
| Top-up | Pre-university (ages 16–18) | University |
|---|---|---|
| €5 | 10 problems | 5 problems |
| €10 | 20 problems | 10 problems |
| €20 | 40 problems | 20 problems |
| €50 | 100 problems | 50 problems |
| €100 | 200 problems | 100 problems |
Problems covered by each top-up at standard priority; with priority, each problem costs ×2 or ×3.
Credit does not expire. Unspent credit is refunded in full, with no fees deducted, to anyone who asks for it within 180 days of the top-up; the refund is made within 3 days.
What never uses credit
Watching any lesson in the list, asking for a problem that is already explained, or a request that is declined.
Explanation level
The same problem, explained at your level
When you ask for a problem you choose how you want it explained, and all three levels cost the same. Each lesson in the list shows its level with the logo, one to three times.
Beginner
For someone coming with the background of two or three years below: it starts further back and takes nothing for granted.
Intermediate
The level of the course the problem belongs to: what is expected of a student who is studying it.
Expert
Two or three years above: more rigour, generalisations and links to what comes next.
Problems on request
How a request works
You bring the problem and receive its lesson, with the same approach as the published ones, in English or in Spanish.
- You send the questionA photo or a PDF of the problem, and you state the subject, the explanation level (beginner, intermediate or expert), the priority and whether you want the lesson to be public or private.
- It is looked up in the listIf that problem is already explained, it is free: you receive the link and nothing is deducted from your credit.
- If it does not exist, it is preparedThe lesson is produced, goes through the quality checks and is reviewed by a person before it is delivered.
- You get an email with the linkWithin the time of the priority you chose, and its price is deducted from your credit.
Two conditions worth knowing
Public or private, your choice. By default the lesson joins the list and is free for everyone. If you prefer, it can be private: it is not published and only those who have your link can see it. It costs the same.
A request can be declined. If the question cannot be read, the subject is out of scope or the problem does not suit this format, it is declined and nothing is deducted from your credit.
Before delivery, every lesson goes through the quality checks.
Want to know when requests open?
Write to me and I will let you know. Meanwhile, every published lesson is yours.