Thursday, May 28 — Day 11

Today's new things: 13/14/15 tables, 2-digit × 2-digit, Oslo era.

Math — the big move

Finish the table: 13, 14, 15 across. (15 × 15 = 225.)

Then the trick that makes mental math feel like a superpower: (a + b) × (c + d) = ac + ad + bc + bd.

Today's worked example:

17 × 25 = (10 + 7) × (20 + 5) = 10×20 + 10×5 + 7×20 + 7×5 = 200 + 50 + 140 + 35 = 425

Same idea, second example:

23 × 14 = (20 + 3) × (10 + 4) = 200 + 80 + 30 + 12 = 322

Both numbers split into tens + ones. Four products. One addition. The whole problem is four times-table facts.

Science — valence as bonding intuition

You know the valence numbers. Now think about what they mean:

• Carbon (4) makes 4 bonds. That's why carbon is the backbone of basically every molecule alive (CH₄, CO₂, sugars, DNA).
• Oxygen (6) wants 2 more electrons → makes 2 bonds (H₂O).
• Nitrogen (5) wants 3 more → makes 3 bonds (NH₃).
• Sodium (1) gives away 1; chlorine (7) takes 1 → NaCl.
• Magnesium (2) gives away 2; oxygen (6) takes 2 → MgO.

Pattern: count to 8. Whatever's missing is how many bonds the atom needs to make (or break) to reach a noble-gas-stable outer shell.

History — the 1970s-1990s peace process

Camp David / Israel-Egypt held. Egypt and Israel have not gone to war since 1979. That treaty is what a peace deal looks like when both states commit and the people in each country are part of the deal.

Oslo I is the failure. Israel and the PLO signed papers recognizing each other; the plan was a Palestinian state by 1999. What actually happened: the negotiations stalled, settlements expanded, Rabin was assassinated, the Second Intifada erupted in 2000, and the situation has gotten worse every decade since. A peace process is not peace, and Palestinians being asked to wait their turn while their land disappeared turned out not to be a recipe for trust. We aren't neutral about this — we don't think the Palestinian people have been treated justly, and Oslo is a big part of why we say so.

Good Friday held. Northern Ireland's "Troubles" were ended by a deal that gave both sides political seats and changed the rules about who could carry guns. It's strained — Brexit complicated parts of it — but the violence is mostly gone.

Today's exam (20 questions)

• 8 math (4 tables 13/14/15, 4 two-digit × two-digit breakdown)
• 1 fraction-add + 1 fraction-mul (review)
• 3 valence (bonding-flavored)
• 4 peace accords
• 3 evolution (dinosaurs + KT)

Warm-up

• 10 problems of the (a+b)(c+d) shape. Pick any two two-digit numbers ≤ 25. Solve on paper, then verify.
• One pass through today's accord years out loud.