An insect crect crawling up a wall crawls ` 6cm` upwards in the first minute but the slides `4 cm `downwards in the next minute. If again crawls up `6 cm` upwards in the third minute but again slides `4 cm` downwards in the forth minute. How long will the insect take to reach a crevice in the wall at a height of `22 cm` from a starting point ?`

Explanation

Efferctive distance crawled upwards in ` 2 mimute time =6-4 =2 cm`
The insect eill craw1 2xx 10 =20 cm` upwards in `2 xx 10 =20 minutes `
In `21 minute ` insect covers `6 cm` upwards and reaches the crevece located at `22 cm`.
:. Total time taken `=20 +1 =21 min`.