请教小五数学题（共2题）

kathyjfxu

1、Fahmi was writing the number 1, 2, 3, 4...... on a piece of paper. He stopped after writing 390 digits. Find the last number that he wrote.
2、A stallholder sold 555 kg of watermelons and papayas. A basket of watermelons weighed 16 kg and a basket of papayas weighted 7 kg less. If he sold 5 more baskets of watermelons, how many baskets of papayas did he sell?

frekiwang

1 - 9: 9 single-digit numbers = 1 x 9 = 9digits in total.
10-99: 90 2-digit numbers = 2 x 90 = 180 digits in total

390 - 180 - 9 = 201 - he wrote 201 digits for 3-digit numbers
201 / 3 = 67 - he wrote 67 3-digit numbers.
1st 3-digit number is 100
67th 3-digit number is 100+ 67 - 1 = 166

The answer is 166.

frekiwang

Each pair(a basket of of watermelons and a basket of papayas) weighted = 16 + (16 - 7) = 25kg
The total mass of all pairs (excluding the extra 5 baskets of watermelons) = 555 - 16 x 5 = 475kg
The number of pairs sold = 475 / 25 = 19
one pair includes one basket of papayas, so the answer is 19.

kathyjfxu

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看了你的答案，豁然开朗，非常谢谢！