Times Market — Lesson 90: Two-digit times two-digit
Game time: Sum Racer →Lesson 90: Two-digit times two-digit on an abacus
Level 7, Times Market. Break the first number, like before. Then break the second one too.
What your child does, card by card
Two-digit times two-digit. 23 × 14: break both numbers. PlayBuddy opens the lesson: “Four small times sums make one big one.”
23 × 4 = 92: break the 23: 20 × 4, then 3 × 4. The beads work the column line by line, zero, 80 and 92, while the sum sheet below lights each line and ticks it; “20 × 4 = 80”, “3 × 4 = 12” and “Together: 92” light up as the total grows. 80 and 12 make 92.
23 × 14: 20 × 14, then 3 × 14. The beads work the column line by line, zero, 280 and 322, while the sum sheet below lights each line and ticks it; “20 × 14” and “3 × 14” light up as the total grows. Two parts. But each one is still big.
Four small parts: 14 is 10 and 4. The beads work the column line by line, zero, 200, 280, 310 and 322, while the sum sheet below lights each line and ticks it; “20 × 10”, “20 × 4”, “3 × 10”, “3 × 4” and “= 322” light up as the total grows. 200 + 80 is 20 × 14. 30 + 12 is 3 × 14.
21 × 13: the abacus makes 200, 260, 270 and 273 by itself, a green ring on each bead just before it moves, and the sum sheet below ticks each line. 200, 60, 10 and 3: together 273.
In Try it a green ring marks the next bead while your child works out 32 × 13 and 24 × 12.
The tiny practice drops the ring: work out 31 × 22 and 43 × 12, each round starting from its own number.
Then the beads hide and the sums 10 × 10, 20 × 10 and 12 × 10 are done in the head, the answer picked from 100, 120 and 200.
You're ready! Four small times sums make one big one.
What this lesson trains
About five minutes and 19 answers. Altogether the child makes 29 bead moves (11 with the top bead, 18 with bottom beads). Up to 682, read and set from the left. Then 3 quick looks in your head. The friend rules here: +2 = −8 +10, +4 = +5 −1 and +3 = −7 +10, used in 3 of 16 sums.
It starts with doing: work out 32 × 13 and 24 × 12.
The sum sheet
The lower window shows the column as a child would write it on paper: one number under another, the current line in yellow, ticks on the lines done. The abacus carries the running total from line to line.
What PlayBuddy and PlayType say
PlayBuddy: “Four small times sums make one big one.”
PlayType: “Break the big number into tens and ones.”
PlayType: “Twenty-three is twenty and three. First, twenty times fourteen. Then, three times fourteen.”
PlayBuddy: “Big part first, then the small part.”
Stars
19 answers: 1 slip still gives three stars; up to 4, two stars.